I own a townhouse in a condo. As is typical in this type of environment, there are rules about what you can do on the outside of the building. Being burried in the middle of the complex, my cellphone coverage is lousy. I move a little bit out of the building, and it is okay.
I bought a cellular repeater after reading some good reviews and checking their fcc approvals. I had hoped to be able to place the "external" antenna in the attic. Second choice was on the deck. After reading the fine print, though, the deck may not be great because the antenna would still be blocked a somewhat, and they say you shouldn't be within 6' horizontally of the antenna without a wall between (cellular signals penetrate walls, but are severely attenuated).
Someone suggested clamping it to the vent pipe, running the lead down the pipe into the attic, then bringing it out then sealing the hole. The antenna is white, as is the pvc vent pipe, so it would be nearly invisible up there. None of the connections would be within the vent, and it would exit probably 6' above the 'wet' part of the drain. This would probably work, but how many rules would this break, and are they significant? The condo really doesn't like anyone making holes in the roof. An alternative to getting it through the roof was to enlarge the hole in the ridge vent cap which sits under the cap shinges, then silicon it up. Since the coax would be going uphill to make the penetration, it should not leak.