We used 1 foot square sheets of 2 inch travertine-looking tile, which made it super easy to cut and fit. In fact, the only tiles we had to cut for the shower floor were the ones that go around the drain, and the ones on the angled side. Here we've sketched out the cuts and numbered the tiles around the drain so we can easily reassemble them.
You can see where we needed to trim a few tiles along the angled side, and create a few half-tiles to fill in the gaps.
After we got everything laid out and trimmed to fit, we moved the entire thing into the hallway, upside-down. This made it super easy to put mastic down on the shower floor and then lay all the tile.
After laying the tiles in, we went back and smooshed them around a bit to make sure all the grout lines lined up and that the tiles were as even as possible and sloped toward the drain. Then we tapped them all down (gently) with a rubber mallet to set them solidly into the mastic.
The finished product! Interestingly, we had exactly one 2x2 inch tile leftover from this project.