Great tool - well done! Just one thing - it doesn't always seem to rotate the blocks (stairs, walls, signs etc for eg) benches when you rotate the selection which limits use with rotate.
Also a couple of suggestions:
1. Add a vertical auto-select ie select pos 1,2 on the ground and the tool will scan up and down for non natural (dirt, rock water etc) blocks and include them.
2. Add a option to ignore non building items (lights, benches and other placed items etc) so that it becomes easy to take a schematic of a building without its contents (especially if a vertical auto-select is added)
Message:An item with the same key has already been added.
System.ArgumentException: An item with the same key has already been added.
at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)