You haven't given us complete info on anything that is comparable.
unknown dipole at 7ft
10m antenna on roof @20ft, vertical?
proposed multiband antenna on roof, vertical?
*What bands do you want to operate?
*Any additional height you can get on your current dipole will improve it.
Your Right I didn't tell the whole story, most of my time is spent on 80 & 40 meters, I don't get home in till after dark so the higher frequencies are pretty dead.
I am considering a Butternut HF-2v (vertical) or something similar and would replace the existing antron-99 with it. Currently I have a "Cobra Ultralite Kid" (Alternative Dipole) antenna on the roof which works better than the fence antenna on 40 meters and is useless on 80 meters. The house is only 40 feet long.
My fence antenna is a center fed dipole approximately 7 feet off the ground (stapled to the fence) each leg is approximately 60 feet and is in a horseshoe shape. the antenna is resonate at 3.900 Mhz the reason I cannot go higher is the Telephone and Cable wires run directly above the fence approximately 6 feet.
Thanks for the help