Toilet on slate...
You can shim it using lead, just fold it over until it's the correct height.
To go a step further (in addition to the shims) and give the toilet a totally flat surface to sit on put some plaster around the edge of it. Put the bolts on and put the toilet down with no ring. Trace the outline of the base of the toilet onto the floor and pick the toilet back up. Put the wax ring on, mix up some plaster of paris and put a generous bead of it around the outside of the toilet. Put the toilet down and snug up the bolts. Have a bucket of water and a sponge waiting and wipe up the excess plaster kind of pushing it under the bowl. You can either make it flush with the edge of the toilet or push it under a little more to give you some room for grout or caulk, that's purely cosmetic though.
Edit: You can use wide masking tape around the outside of your toilet outline to make cleanup easier.
Last edited by Tmb9862; 06-05-2007 at 07:36 AM.