Ivan Vegvary wrote:
Inherited a bathroom project. Basement, slab floor, shower pan installed
(32in x 32 in) already installed but on a slope. It is about 3\8 in. out
of level. My odc prevents me from not correcting this even though it does
drain. Three options.
1. Pull pan and level concrete slab.
2. Pull pan and carve away on fiberglass ribs.
3. Pull pan and shim (possibly roof shingles) floor.
All advice appreciated. Note: There is no shower stall yet. Just pan
with surrounding studs. Pan has not been affixed to studs.
Ivan Vegvary

A variation on Option 1, unless this is what you meant by "level concrete
slab"...

Pour a bed of mortar and press the pan into it, making it level. Use enough
mortar to fill the voids below the pan and make it feel very solid. If
you've ever stepped into a fiberglass shower or tub with voids underneath
and felt the give, you'll know what you are trying to avoid.