- A Binary Space Partitioning (BSP) tree represents a recursive, hierarchical partitioning, or subdivision, of n-dimensional space into convex subspaces. BSP tree construction is a process which takes a subspace and partitions it by any hyperplane that intersects the interior of that subspace.
The first step is to define the level size, and then start subdividing to achieve room grids. This first gif shows the sectioning taking place. The prospective room will need to fit inside of the grid section, room size being dictated by the room walls proximity to the grid subdivisions.
Additional reading on BSP and general PCG room generation: