In our current home arrangement my kids share a bedroom, and have a separate toy-room. The spare bedroom is my dearest's sewing room, although it often reverts to junk-room state. We use the dining-room as a kind of study.
My son would like a room to permanently set up electric train tracks. The toy room isn't big enough so he uses the floor in the "good room", but we make him pack it up at night.
I have said for some time that I would like a home dojo (martial arts area), preferably in a basement so as not to frighten the neighbours. As something of a homage, I would call it The Dungeon.
Additionally, there is the prospect of "doing science at home". Now, when I did year 12 chemistry I was fortunate to have a skilled laboratory partner, Steve Alcorn, who led the experiments while I took the lead on the calculation. However, my general experience at school and later at Uni. was that lab. work was dull, except on one occasion when I re-designed an experiment to make it work. That was a blast; the creativity and imagination were re-injected.
Reading Oliver Sacks's memoir Uncle Tungsten conveys the joy (and obsessionality!) of designing and performing one's owns experiments. In my case, as a teenager I satisfied that desire in the more abstracted world of exploratory computer programming, but I would like to expose my kids to the more concrete worlds of chemistry, electronics, and -- probably -- robotics first. Biological experiments can wait until they are older!
Apparently chemistry sets don't come with chemicals anymore. Here's a link to The Illustrated Guide to Home Chemistry Experiments, which sounds like a great place to start. Apparently you can get in trouble with the authorities for daring to do Science at home, so perhaps I should secrete "The Lab" behind the Dungeon.
Of course I don't really need a bigger house to do all this great stuff, just time, a little discipline (for cleaning up) and more importantly the patience to wait for the kids to show sparks of interest. Here's a nice story of a parent engaging a child in learning. For now, I'll try to encourage the kids to keep messing around with play-dough and paints, and try not to gripe too much about the mess.