We're glad you’re thinking about this before you build your dome. There’s a lot of alternatives, based mostly on the intended use. The easiest and least expensive is to use an army surplus parachute. Just remember that parachutes are like giant umbrellas and they'll definitely catch the wind.  The hardest way to cover your dome is to individually cut triangles out of wood, polycarbonate, Styrofoam, or sheet metal.  There are also templates for covers, where you plug in your dome diameter and it will measure out the ‘gores’ (pie-type sections) that make up your cover.  Sonostar has a limited supply of shelter covers and greenhouse covers that fit 24’ 3V 4/9 domes, and we order a lot of custom-sized event dome covers, but they take 4-6 weeks for delivery.