Spring RTS Engine

Basically, what I'm asking for is this:

If building a unit will put your storage (of energy or metal) at 0 or below, do not allow the building of this unit. This may be already possible in this version or the next using LUA - if so, how?

Workaround, provided you don't have ressource costs: Make the size of one nanopacket exactly the amount of storage you'd need.