Each square is 500 x 500 x 40mm. 5.0 out of 5 stars 1 rating. Simple to install, the Ecogrid 7x4 plastic shed base can be placed straight onto grass, dirt, decking, patio or any other hard standing surface and provides a solid raised base for a garden shed, summerhouse, playhouse or garden building. Gravel Grids. Y ou can fill up the spaces with stones, bark or whatever you would prefer . The sheds feature robust framework for a sturdy construction and heavy duty roofing felt to keep your possessions protected from the elements.