I have an existing 6’ x 4’ garden shed sitting on a concrete base. I want to replace the existing shed with a 8’ x 6’ shed and existing concrete base isn’t big enough. I don’t want to dig up and lay a new larger base, so what’s going to be the easiest way to extend the base. My thinking was just to extend it using slabs around the edge of the existing base at the same level. Does this seem reasonable or am I likely to get problems with the slabs sinking at a different rate from the concrete base?