I'm 99% sure you can build you own bin, just set it up with x2 4" cam lock fittings for auto delivery (Supply/vent). A slide in hatch high on one of the sides is good for self loading as well. A local installation guy I was talking to said he made them out of plywood with the Zip system and the green vapor barrier on the inside. He would seal up all the seams with the zip tape. That way the inside was more "slippery" to allow the pellets to slide down the tapered bottom to you auger better (or vacuum system). It also gives moisture protection to the wood if is sweats. Insulating between your studs is a good idea as well especially if the bin is outdoors. I found standards on how to build your own somewhere on a European site. Other than some metric conversions (unless you're from Canada!), it was pretty well laid out for standards of sloped bottoms etc. Only difference is they use 100mm Stortz connections vs 4" Cam-Locks for standard delivery connections.