I would appreciate any suggestions about photographing an old, very large concrete / steel warehouse roof in downtown Fort Worth, TX. the reason I ask is others have tried doing so but from the ground and each attempt has failed. Once over the roof and out of line of site the drones crashed, not sure what brand of drones (the building is over a city block long and 8 stories high) - it is assumed the loss of control once drone was up over roof was due to the heavy concentration of steel in the building - our plan is to shoot from the roof and walk along with the drone (P4) as we photograph the roof - even with this approach I am very concerned about compass interference and calibration issues - s you can see its a monster - when on he roof, the parapet walls are 6' high - so i will be surrounded be steel and concrete - insulating the p4 from all that steel before take of is another issue