Hmmm... aluminum... possible aluminum oxide on each joint = rectification = angry neighbors as the others have stated.
Hell, toss a dipole on the edge of the roof (or the top even) and call it an ice melter if you live in an area that has ice in the winter.
But I would put it on the peak of the roof... but that's just me.

Did you know that aluminum filings and iron filing and (XXXXXXcensoredXXXXXX) are the makings for a great Termite b--o--m--b? Very powerful and hot as all get out.
When you are running power to the rain gutter notice (carefully) if the aluminum oxide at the joints is glowing? If so... stop transmitting immediately...!
If you go to the peak of the roof method you may get some directionality by make a semi-inverted Vee running the antenna center at the peak and the 'legs' from the lower point of the rafters.
Always have the feed point at the highest point possible.
ie:
roof edge (outer edge of rafter)
_ _ _ _
\
\ antenna
- - - ridge pole (peak of roof)
\ antenna
_ _ _\
other roof edge (outer edge of rafter) Do bass ackwards if directional (see below)
If you go this route try to get wire that has a plastic insulation with a similar color of the roof shingles. And the coax... well hide it the best you can or find some soft plastic tubing to match the shingles (might be expensive <sigh>).
I don't know what wave pattern this might give you... a true inverted Vee is pretty most like a vertical in its wave pattern.
Anyway have fun.
PS. I have wires every where... why? My morning Glory flowers need them to climb on... in the winter no one even notices
