Preparing greenhouse beds

Just down sized to a lovely bingalow and hv treated myself to a large Rhino greenhouse. I want to grow some crops in beds inside the greenhouse but the ground is to awful for words. Talk about builders rubble.. boulders bits of wood plastic banding you name it and it down in there. so far I have dug down 18" and  removed the clayish soil in 2 ft areas, seiving out stones and debris and breaking down the clod like bits of clay as i am told its nutrient rich.  I add blood, fish and bone and leaf mould then refill the cleaned soil and cover it with black soil membrane. I will have to do this to all the soil I think.  Am I doing the right thing