I am in Newport Beach, CA and routinely pick up trunked operations from San Diego, CA with a rubber duckie on a Uniden BR-330T. I probably have some degree of line of sight, but it's still gotta be over the horizon from here.
My concern would be if there's any metal flashing covering the outside of your roof. Otherwise, a gain antenna up there might help.
I used one of these once years ago with decent results:
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They do have an 800 MHz version - VT-800. You just gotta figure out how to get the feedline in without getting a leak, or getting caught.