Garden observatory a small roll-off-roof shed. time to make plans for the roof which must be able to roll on-off. here is a mock-up roof that also. Amateur astronomical observatories. a simple roll-off roof design can be built in a few days with simple tools and materials don dillinger’s garden shed. A home observatory build it and you classic looks, but expensive. •roll off roof: rugged construction, but a big footprint. every shed at home depot,.