I've been thinking of ways to do the bottom floor in the tower.
I like the idea of hexagonal flagstones here. They're an organic shape, my enchanter likes to study the natural world, and they echo the shape of the tower.
I printed off a hex grid in the right size (from this site - they do a brickwork graph too).
Then I rolled out some air-dry clay (I love Paperclay but I found a less expensive one in an art supply shop - it has a different feel but works well) on a plastic sheet.
I put the paper grid lightly on the clay, and pricked holes with a pin at all the corners of the hexes.
With a piece of fine veneer (strong card would work but you'd have to replace it every so often to keep it dry and clean) cut to the length of the grid lines I pressed it into the clay halfway through, using the pinholes as a guide. Otherwise known as 'join the dots' :D
Then I tried a second test, pressing all the way through to the bottom, so that when it dries the tiles will be separate. I'm not keen on having to deal with the clay cracking in a large sheet.
Now to wait for it to dry . . .