So I became the Stonemason Guildmaster, but other than collect money, what do I do with it?

I see that there are upgrades and all that normal stuff, but apparently it has a separate money source from my own funds, so any time I try to buy something I'm told there are insufficient funds. How do you improve your guild house?

In one of the rooms you can click a spot that lets you donate money to the guild. This money can be used to make the improvements.