Hidden passageways in all the rooms. Every room will be connected via an intricate maze of crawlspaces, slides, ladders, and all manner of hidden passages. Sure i could use the stairs like a normal person to get to the living room, or i could pull a book off the shelf to reveal a trap door in the floor that leads to a slide downstairs.

Mine is utterly mundane: I want one of those little tower nook things like on Victorian houses. I think it's just called a turret?

A cheese room. With lots of cheese. Different kinds, different ages and from different places. But still only cheese. I fuckin' love cheese!

A Bath Room. No, not a bathroom. A room just for a wide bath, with a fireplace, a window overlooking greenery. A sound system of course. There'll be a small bookshelf for a choice of relaxed reading, and possibly a fridge at arms length with a choice of relaxing drinks.

I want a hidden control room, where I control the internet, piped in music, cameras, security and other automations of the house.

In this way, when there is a complaint of something not working, I just disappear to that room and tinker to my heart's content. Problems mysteriously gets fixed (by me).

This should be a nice and comfortable room, with plenty of space, a bathroom and a skylight.

A walk-in terrarium room.

I want a nap room. Not to be confused with a bedroom, as the bedroom is for sleeping and a nap room... well should be self-evident. Nice climate control, piped in white noise type sound I can change easily (From regular white noise to rainy background to sounds of the woods to lo-fi chillhop), and multiple things to nap in, a hammock, lazyboy, and couch at minimum.

A landing strip for model aircraft with lights.

A huge garden/green house in the center with fruit trees and berry vines, etc. and in the center of that, a sort of pool/pond. The whole place has a path circling through it with various benches and seats and musical instruments on display/for use. Piano, harp, hurdy gurdy, etc.

Pneumatic tube system. Brass steampunk shit like in old banks and skyscrapers would be fine, as would clear plastic ones like drive through pharmacies.

A bathroom with a urinal.

A secret passage. I've always wanted one. My parents built their home and I was genuinely disappointed that they skipped this vital element.

I want to build a stadium-sized structure with a retractable roof around my house.

An underground gymnasium. Not a dinky one. Moreso what you have in a high school. A whole bunker facility would be nice as well.

A hidden elevator that leads into a batcave-like place but its just a place for me to play video games without the kids interrupting

A wife.

A Roman style inner courtyard!

A music room, with space for my decks and records, top notch sound system, perfect soundproofing on the walls, a lighting system, a small dancefloor, a bar. Also, it would be hidden behind a bookshelf, as described in OP.

A built in, small walk-in refrigerator with TARDIS doors. I want it to be bigger on the inside.

One of these things.

One long stairway only going up, one even longer coming down, and one more leading nowhere just for show.

A tower. I'm dreaming of it since I was a child and it's weirdly specific, made from wood with a stone base to the first floor, and the roof has a mechanism to unfold a 1-person balcony. It's not to be above other people, it's more like a "I'm seeing everything but I'm safe and only I can decide who's getting in my tower" -thing. Plus: I love wind and fresh air and hate the feeling of being underground or even trapped in a box. Would base jump and day, but would not set a foot into an underground mine if you give me a million dollars. Some day I'll have a tower... Actually waiting for the land prices around here to fall a bit to buy building ground, no joke. Don't know if my wife says yes to doubling the house building money for a meager tower though, lol

A tunnel, as in a disused railway tunnel. Could build in it - rooms, short corridors, leading to other rooms, other corridors - on and on as long as money and cheap building materials allow. Fill it with disturbing symmetries: same objects in the same places over and over. Maybe a giant isopod in formaldehyde.

I know music producers have like a room where almost no sound can leak through. I want a room like that. If I'm ever overwhelmed I'll just go to my quiet place :)

I’m not sure. Perhaps an art room, a room specializing in every art tool known to mankind, for anyone who is an artist, so they don’t have to return home to make or finish a piece.

I have bought my dream house. It's old, cranky and somewhat scary. Now I only need the money to be able to return it to its former glory.

What I would want to add to her would be a few hidden compartments, one or two small root cellars to store wine and some balconies. If I really had the money, I'd modify the roof and build a small greenhouse/sunroom, big enough to put two chair and a small bookcase, after stuffing it with plants.

I'd have a room dedicated for porn basically. Monitors playing films 24/7, posters on the walls, toys, clothes, dolls etc. all over in huge quantities. Basically if there's a "kinky version" of anything I want it there instead of the ordinary thing. Like a light switch that's a dick you flip up and down etc.

Smash room. You know what I'm talking about. Find an old TV? Smash it! Whats this someone threw away a perfectly good pinata? Smash that sucker!! Get yourself a controller because it's time to play Smash bros!!!! He'll I'll even put Smosh on youtube, it sounds close enough!

A cube. A room you enter and every wall, the floor and the roof is projectors or monitors. Displaying a 360 degree video of an environment. Like a forest, on a boat, on top of a mountain. It plays ambient audio fitting to the theme. And I can just lie in the middle and meditate and enjoy.

Probably pointless now that we can do the same with a VR headset. But in that room you could share this with others while also seeing them.

A room with perfect everything.

I used to be a painter and did some construction. You would not believe how much I want a perfect room. It's basically just like Morty on perfectly flat ground; most people wouldn't get it until they were in it.

I'm talking: sub, foundation, frame, crown, base, millwork, frames, drywall, paint. Everything is meticulous and perfect.

The ground is perfect, the foundation is extremely thick, high gyp, super high quality, perfect. The framing is made of perfect ironwood, no flaws, is perfectly plumb, and is extra thick and rigid with those corner things; the room could be spun by a giant like a basketball. Perfect insulation, the absolute most incredible stuff and a ton of it, like R2000 and perfectly sound insulating -130db down to 0hz. The drywall is six layers thick, all of the corners and curves are perfect with the finest, strongest compound; it's super smooth and the angles are all perfect because the framing is perfect, because the foundation is perfect, because the ground is perfect. The walls themselves are totally smoothwall, no texture whatsoever, it's like touching a sheet of metallic plasticized glass, but really it's just the extremely evenly applied dozen layers of the most advanced exterior coatings known to man; in not going to name names, but it's fine stuff. All of the coatings on the walls, any millwork or cabinetry, and even the floors are all extremely high brightness white, the whitest white; the stuff that actually kind of glows because it's converting some uv light to visible spectrum and is basically just pure titanium dioxide suspended in a crystalline structure. There are no chips in anything. No dents, no scratches, no fingerprints, no dust, no oil, no stains. Perfect. It's well lit with natural light, and augmented with locational, directional, intensity, and temperature active diffuse lighting. The air is perfectly controlled and can have a constant flow of fresh, new air, or to have little to no airflow, depending on what I need in the moment - because having anything be possible on a whim takes the right resources. Sunsets, mornings, afternoons, overcast, nighttime, storms - every setting and energy and vibe is increased tenfold because the room is perfect.

And in this room, nobody goes. It's my room to be made by me, to be in, to have. I will know everything about it because I'll have made it myself. The real wealth in this life is the ability to do whatever you want without consequence, because time is the real currency and we must all spend wisely - wealth, though, allows you to spend recklessly because, despite what's seen on the surface, true wealth affords you to not waste time on being poor and having to work for others with small margins to save: the hours most people spend working and toiling are hours I would spend pursuing projects that are fulfilling to me...

Like the perfect room - an eternal dessert for one's existence.

A secondary "dirty" kitchen for butchering and so on, designed to be hosed down for cleaning. It would also probably have a walk in freezer, and that probably counts on its own.

I want two basement levels (at least).

So many special things are possible in that different climate down there.