It's a little late now but I have a good tip for people who are building runners/skis for their shack. I just built some for my 8x8 shack. What I did was take 12 foot 2x4s and attach metal roof flashing to the bottom. It's a roll of sheet metal about 30 some feet long and maybe 10 inches wide. My shack probably weighs 600+ pounds and I can push it around by hand using these metal bottom skis.