As has been suggested several times over the years and most recently in
http://www.mangband.org/cgi-bin/yabb/Ya ... 74;start=4
As suggested in the past, let players build castles. If they find a level in the wilderness, they must first buy the entire level for a massive amount, THEN they can build whatever they want there, a normal house with whatever dimensions they'd like or pick a number from the vault list.
I'm not sure if the wilderness levels layout should be changeable, in a way I think I'd prefer not. It'd be more fun to run around the wilderness trying to find a great looking level, maybe with some small lakes, maybe some mountains... Since you can recall to any random wilderness level I don't think the prices should vary a lot, though they should be higher in the immediate area around town, maybe up to 5-6 levels from town, since this would allow people to visit their levels more easily.
Historically, wealthy families owned lots of land and at least one great castle, so in a way each wilderness level should probably not be insanely expensive, I think around 10M would probably be right. Maybe 20M or higher for those closer to town. 1 and 2 locations from town would still be the way they are now, with some small and some larger houses, but not directly buyable. There'd maybe be an outer town wall outside this.
But the castles themselves should probably range from at least 2-3M for the smallest ones and up to maybe 100-200M for the huge ones. This seems kinda historically correct.
I'd guess there's at least 1500-2000 wilderness levels out there, so there's plenty of room for everyone.
How about just adjusting town houses in a way similar to what fink_mage suggested, make it so that each player can only own one town house, all town houses have reasonable sizes, ranging from rather small, maybe 2x3 or so up to somewhat large, maybe 6x6 at most. And then the first and second level around town could have fixed houses, maybe west of town would be with larger houses, for the rich and east of town smaller houses for the poor, and so on? And then outside of that again people could buy entire wilderness levels and build custom sized houses or vaults there, if they have the cash.