I want to make this building in a map I have no idea where I would begin on how to make this building shape. I tried making an arch, however I was stuck on how to make the front/back walls to cover the arch holes. I attempted by merging the inside vertices of the arch into one but it created an invalid brush instantly. I don't need the front/back faces "pushed in" like in the picture So how can I achieve this and is there any optimisation I can do to it other than making it func_detail? I'm terrible at making complex shapes like this and I recently began making a proper map so yeah, sounds impossible.