I was bad at building, but over the last several years I've made some builds that I'm very proud of. Being a perfectionist does NOT help at all. I don't participate in freebuilds or Fort Wars often because of this. I just can't make something on demand.
To remedy this, I actually devised two strategies. The first is recreating buildings or structures I see in real-life. The second is something I like to call "prototyping." I build something, typically a wall, hallway or structure of some sort, then I duplicate it over and over and make incremental changes, multiple designs, until I found something I absolutely love, or I just pick the best looking one. That's how I built the spawns and bases for Battle for Snowy Hills, and the spawn and weapon shop in my Trench Wars server that I plan on hosting soon. I can post some screenshots of this if you want.