Have you ever watched face off? you could build a muscle suit like they do. You need platsil gel-10 which is a skin like silicone, modroc plasters, a lot of plastiline ( oil based clay), sculpting tools and a lot of patience.
-First thing first, make a mold of the body part you want ( like chest ) using modroc plasters
-Make a copy of your body part by pressing the clay in the mold
-Sculpt the clay as you like
-Make another mold with plaster
-Pour in silicone ( gel10) and wait for it to cure
-Enjoy your custom muscle