Over many years of doing this business, I have found the most effective way to place squirrel traps on rooftops (or ANYWHERE baited traps are used) is by using trap shelves. Trap shelves have holes drilled for attaching traps securely with spring hooks from Doug Fields.
There are multiple reasons. First off, it may take an extra few minutes to mount the shelves, but it is a time-saver due to how fast you can swap traps when using the spring hooks.
Reason 2: Squirrels will coat the boards with urine and feces when caught, creating an attractant far more powerful than any bait or lure.
Reason 3: Traps not secured will often misfire due to squirrels moving/jiggling them as they try to get to the bait from the sides or back. Securing traps with the spring hooks (or even wiring them) will almost eliminate misses, as the squirrels can crawl on the traps, paw at them from the sides or bump/push at them with their nose and the traps stay set. I have observed squirrels *working* traps for many years, which is exactly why I secure ALL squirrel traps, unless they are set in soft dirt and can be bedded in solid.
Reason 4: Bait stays in the trap. Doesn't fall through the wire if using peanuts, corn, etc.
Here's a couple pics showing the very simple trap shelf set-up. You will notice I even use the trap shelves on the ground. Again, cuts down on misfires and the boards hold the scent from urine and feces.
The board (shelf) below the meter is actually upside-down in this setting. I attach a small board along one edge, and for setting rooftops the board is what makes the shelf level (or close to level). I have them with varying heights on the leveling board.
The spring hooks are designed for gutter mounting (to gutter support brackets) and work perfectly. Usually have to use a 1/2-piece of bread to hold bait from falling through the bottom of the trap. I'll apply some peanut butter, then dab in some sunflower seeds, peanuts, or corn.