Current home is about 1500 square feet. There's three of us living there, me and two roommates. Sometimes I think it would be cool to get a bigger house, or add on to the one I have, but even now, there are three rooms that mainly just accumulate junk. One room upstairs has a weight bench that one of my roommates uses from time to time, but mostly it just collects junk. That room is about 10x15.5 feet. Downstairs there is a small office with a walk-in-closet, and, hate to say it, mostly junk. Probably about 7x15.5 feet there. And then, an enclosed side porch that's about 7x10 feet. There's a second fridge out there that gets used, but other than that, it just gets packed up with stuff that we rarely use.
I'd really be better off simply getting rid of stuff, rather than trying to add on to the house. My only real complaints about the house are 1) it only has one bathroom and 2) it's fairly long and narrow, so while none of the rooms are really tiny, none of them are really huge, either. The living room, for example, is only 13x12.5 feet.