anyone else done such concrete tops share some insights?

My contractor does it by driling metal rebars into the wall, and use plywood for the molding..after curing///then only use red brick for the leg

i am referring to bathroom sink vainty

my plan is to tile my vanity, but hate tiles punya joint lines...so i need to find one big piece of tile big enuff to cover my length of countertop.
After that how to tile the leg without joints....haha i am clueless