Limiting Buildings / Units

Does anyone know how to limit the number of a certain type of building or unit?

I've tried something along the lines of detecting multiples and destroying one and refunding the resources... but havent had much success... any ideas?

It would help if you were more specific. What you have asked for could mean one of several things. Please explain in detail what you want so others can help you!

Theres a trigger under Player i think, which is something like "Limit construction of unit type to X"

Thanks Pheonix-IV and Alevice for a helpful answer

I gotta re-install WC3 but when i do that sounds like the perfect solution