Whenever I make them they always turn out ugly.
How do I blend them perfectly to the terrain?
And yes, I did use the search function, tyvm.

None.
How do I blend them perfectly to the terrain?

ForTheSwarm

NudeRaider -- blessed innocent soul knows nothing of the strife we had before EUDs were discovered 
DarkenedFantasies -- Probably just didn't care. For example, at some point before release, they've updated the graphics of some of the Protoss buildings (Forge, CyberCore, Citadel, Observatory, Arbiter Tribunal), but instead of properly re-rendering them with edited 3D models, they did crappy copy-paste jobs on the rendered graphics.
Oh_Man