Also, is it possible to have a limit on how many of a certain building can be built, eg I might want only one robot scientist buildable for the entire empire or maybe one per system. I guess it would be treated as a wonder perhaps, although I don't know if there is code for wonders yet.
Good question, I don't know the answer.
We didn't really design the whole buildings model yet, so tzlaine has only really implemented the effects parts of them, and the basics like name, cost, build time, and maintainance. I think I whined about this at one point, but it never got done really.
There's actually a fair bit more we need to add to the buildings model from what's there now... such as:
Prerequisites for buildings (other than techs), such as presence of a special on/in Planet/System/Empire/Galaxy (or a more complicated resources-access system, which would be later extended to include resource trading), various properties of P/S/E/G in which building can be built (environment type, star colour, population, meters...)
Limits on number of buildings of given "building stacking group" in certain range or by number in P/S/E/G
How do deal with unpaid maintaiance or various other unmet-after-being-built prerequisites or conditions, perhaps with some property that effect conditions can acces to turn themselves on/off appropriately, like whether a building is "Enabled" or "Active"
Some form of obsolescence? tzlaine's forthcoming effects to alter building descriptions might do this