From what you have said and from the game page on itch it seems like I have all of the current buildings or at least most of them.
Having died on my first journey down the Path of Chaos I find myself wanting another way to get hammers.
So I have an idea for you that fits with the genre:
Alchemy.
All items would need to be ranked and then given a percentage chance of successfully changing one type of item into another.
Changing wood into stone or creds into XP would have a high percentage, but turning wood into a small Soul Room would have a very low percentage and 1 cred into a hammer would also be very low.
As far as upgrades for the building go,
Percentage chance could be increased.
Time to completion could be reduced.
Options of what can be transformed could be added.
You get the idea, I'm sure.