TBH, I don’t use the option to create custom buildings very much because of the bugs in its current state. I’ll just build, say, a Dining Hall, and then remove the tables and use it as another building type, like a crafter’s house or a storeroom. This is a thread for ideas for more prefabs since we desperately need more. 
- Barracks (Improved version of the Dormatory. 4 beds, but with a couple of tables and 4 chairs and storage)
- Warehouse (Lots of storage. Crates for Ascendancy, Pots for Rayya’s Children)
- Crafter Buildings (Trapper, Blacksmith, Tailor, Herbalist, etc.)
- Dining Hall with Kitchen (Much like the House for One and House for Two, just an improved Dining Hall with room for an attached Kitchen)
- Town Hall (Not sure if this is a good idea or not since everyone has their own idea of a town center, but a standard central building for your settlement for those of us who aren’t builders. Maybe 8 Tables and 16 Chairs, and a small tower on front.)