what type of silo is it? the old concrete block or is it a newer metal type like a harvastore? i have seen a few that had cellular equipment placed on them, in that case its a win for you as those generate money on a monthly basis. if not the guest house/observatory idea would be something i would consider. the metal harvastore type i think would be very hard to convert into something else, but i believe there is a company from canada that buys thos type silos from you and they re-furb them for parts. if it still has the unloader you could always sell that, although not many dairys use upright silos these days.