I am installing a shower in my bathroom, which is in the first floor of my house and has concrete slab. I have to build a platform for the base of the shower. The platform has to be almost 12" over the slab to be able to fit the trap under it. My question if it is possible to place the trap about 24" away from the shower drain to reduce the height of the platform. Please advise.

To extend the trap from underneath the shower to the horizontal drain line would change the trap from a "P" trap to a running trap. You will have to check local codes to see if this is allowed. Good luck and let me know what they say. Tom