I'm about to start a self build garden home office of 3.5m x 4m - For the foundation, before it there was a large outdoor summer house there on a concrete base. The concrete is not a smooth finish, but a rough edged finish to the surface. My question is, I know the concrete is suitable and strong but as the surface is a rough finish whats the best way to put my wooden base frame down on it? Will it be ok to set it on there or should I still look to raise it? My thought process was water sitting on the concrete and the wooden base just sat in it?