I know that the game will lag when there are too many units on the map. This happens frequently in all those crappy zombie maps and some of those test of survival maps. I always assumed this had to do with a lot of AI routines needing to be updated at once. The question is, however, will the game lag from lots of buildings? Put too many lings on the map, it'll lag. But what if you put a couple hundred or so pylons? Will that cause lag? Or do buildings never cause lag, even in high quantity?
They would not lag but not as much, clicking a pylon in a large mass of course will make you lag. I belive as long as your building doesn't have any animiation or movement the lag will be minimal.
Nothing beats testing.
I doubt buildings give lag at all, and units give so much

try playing evolves with people who wont stop getting air units then its like they attack, or you attack them and all you get is worse lag than a lagger in the game who slows you down.
P.S. I hate evolves maps now.
I think we all hate evolves maps now. Too laggy. Plus, air evolves always end up using valks and sairs, making the player who gets them last invincible. Anyways, after a test, I concluded that buildings don't cause lag, unless you click on them. Granted, I only tested it with a mass of pylons, and when I clicked on one, it lagged while it displayed the aura. Haven't tested with others yet.
it SHOULD only lag with pylons seeings how it uses a TON of sprites..
Yeah. I just tested it with Supply Depots, and it only lagged for a second when the game started up. No lag after that.