Hollow core INTERIOR doors can be cut down to whatever size you desire. Want to take a six panel masonite door and create six tiny single panel doors? No worries, it just takes a bit of skill, glue and clamps. I have worked at a millwork shop and we would take hollow core doors and make all kinds of crazy shapes to fit whatever the customer needed. This included clipping a large piece of a top corner off (at the pitch of the roof) to fit in tight attic renovations. Cutting doors in half to make knee wall or understair access (we did hundreds of these and shipped them out prehung, with a reworked frame and hinges, easy money) , and cutting doors to odd widths, or intentionally making them horribly out of square, to replace a damaged door in a crooked old house. the basic concept is easy. Cut the door to the size you desire, install a new piece of pine to fill in the edge, generously coat the new edge with yellow glue, position the filler properly, clamp until glue sets. Clean up dried glue with a chisel, dress up edge with a hand plane and a touch of sandpaper.......that's all. Hollow core doors are junk, they have internal reinforcement made of cardboard, and the edge fillers (rails and stiles for the true woodworkers among us) are one step up from cardboard in most cases. If you rebuild the door with a nice straight piece of 3/4" pine, it is often a bit sturdier that it was from the factory. Steel doors and other types of exterior doors can also be reworked to some extent, but it can be a lot more involved. Hope this helps.