I have thought about doing brute force raycasts, but raycasts are not free and you would have to do hundreds or thousands of them and may still miss holes or things just out of range. If you built a big 10x10x10 or 20x20x20 room, but left off a wall are you inside? It would block some wind or rain, but you would still freeze if it was not fully enclosed. Say you built walls of center poles, columns or other partial block shapes, they would probably be seen as solid, yet they are full of holes and not really make you inside.