So I'm literally sitting at work right now with a dozen post-it notes (perfect squares) that I've then folded half of them into equilateral triangles. Trying to determine interesting ways to use triangles in walls and still work with triangles to make large areas. I've put together one interesting pattern to make a 90' angle with a mix of squares and triangles. Yes, it required math and yes, I could have just used math or MS Paint, but sometimes it just faster to use physical objects and spot check my math. My last geometry class was over half my life ago...

The pattern is:

Square -> Triangle -> Square -> Triangle -> Triangle -> Square -> Triangle - > Square

The first square and last square are "aligned" in the same direction. This lets you create an interesting corner on a "roundish" wall and keep it aligned to a square castle in the middle. The square before the last triangle ends up making a bit of point and ruins the "round" effect, but call it an architectural embellishment.

Back to doing some more math now. I THINK it's even possible to line this up so both the first and last squares are "lined up", so you could fill the whole thing in and not have a hole