Painting floor tiles?

Any suggestions on making paintable grid based surface like in sims? where you can change floor tiles?

 

make each floor tile a separate object. This is not as bad as it may seem, since unity (pro at least) will batch the meshes that share the same material before rendering so you will not suffer too big of a performance hit there. (so I have been told). Having each tile a separate object will make your life a lot easier in terms of changing floor tiles. I would try this approach first.