Ok first you have to figure out what the value in your area is,very important you have to find out if the compressors are screw type or semi herrmattic,I have been doing a/c commercial recycling for twenty five plus years,manny large commercial units have semi herrmattic compressors,not mention in the other posts,screw compressors are the type that most central a/c units say 4-5 unit tons commercial units are only bigger,semi herrmattic compressors look more like a car engine,semi herrmattic have no copper windings in them and there value is HMS 1 (steel)I would guess that they were left on the roof for that reason,I do agree the only way to get them down is with a crane,you also have to find out how far in the crane will have to go for the pick,cranes have jigs on them that can extend there reach,the cost for a crane in my area is around two hundred bucks for two hours But keep in mind the crane company will start charging you from when they leave there barn (travel time) to and from.hope this helped you good luck