What type fill is best to look out for when needing to raise ground for a shed. Need to raise ground about 2 foot that the shed will be going on top of. Will be hiring out a vibrating roller to pack it in layers. I can get free stuff with stone (2 to 4 inch stone) in it but also subsoil type stuff mixed in also which came out of where a local farmer dug for a underground slurry tank.