Total posts : 45366
It doesn’t sound to me like you need guy wires with 15 ft of heavy 2″ and 1 1/2″ pipe if it is very solidly mounted to the roof, but guy wires are always a good thing.
If you use guy wires, I recommend you ground them to the mast pipe (which in turn should be well grounded). As we know from Rich’s excellent posts in this forum, ground wires will radiate a big portion of your signal. The guy wires will help to add open wire out there on the ground side.