One zip: all levels, as you can go on working on them, and with them the inked sheet, a copy with the rooms numbered, and a key to them in words with your notes, and a copy with the notes numbered. The generator's Export makes the same file, so a generated map opens here too. A file can also be dropped on the sheet. Opening is one step: Undo brings back what was there.
You work in pencil, and pencil can be changed. In a building, walls that close shut in a room; the stone tool cuts into walls and adds to them as the rock tools do with rock. When the pen has gone over it the sheet is done; going back to the pencil starts a clean copy of the same plan. A stair or ladder between two levels is one thing: it lies on the same squares of both, and is put in or taken away on both at once. The plan is kept in this browser as you work, and can be saved to disk as a file. The manner of drawing follows the hand-drawn maps of Dyson Logos, whose own work is at dysonlogos.blog. Maps that draw themselves are next door.