In another game I played, Mystic Realms of Alhanzar, players could design their own guildhouses, but they had to pay real money to have them built. The prices were very reasonable: there was a base cost for a \"minimum package,\"
additional costs for more stuff: added square footage, more rooms/features, etc. Thus players in a guild could chip in together to buy a guildhouse. Since this game is graphics-intensive, you could easily add in stuff like tapestries, paintings, other decorations, secret doors, etc etc, all for a modest fee.
I forget how they worked it if one of the contributing players left the guild; I think they left it to be worked out among the guildmembers.