What exactly are you trying to do? Are you just relocating the coop, or are you wanting to make it mobile like a chicken tractor?
I made a 4x8 footprint rabbit tractor and had it on 10" pneumatic wheels, it was a PITA to move it manually on even short grass; mainly the issue was resistance on the grass, larger wheels may help in that situation, such as bicycle sized tires. If there's a slope, good luck! Pulling with a tractor/ATV/mower would be much smarter if you can.
If you just need to relocate a heavy coop, I'd try making "roller bearings" with PVC pipe or "peeler cores" (round tree stakes) etc. and push it around like they did for building the great pyramids. Alternatively, I just had my HVAC replaced this summer and there was no way to crane in/out the units, so the crew used OSB plywood sheets on the grass and furniture dollies to manually roll it through my property.