hi,i am building a 4ins block shed at bottom of garden, my next door heighbour has all ready built a block shed , the wall his side is right on the boundry, with his footing about 6 ins my side, would it be in order to put my footing 6ins above his footing, and 8 ins wider, there will be a minimum gap of about 3 in between our walls, with a plastic membrene in gag to keep out any damp, or could i cut his footing flush with his wall, i have 9ins disc cutter with diamond blade, i wan,t to keep tight as i can to his shed ,to minimise any loss on my side, many thanks for any help.