Check out www.bestbuypoolsupply.com/solar-heating.htm. Click on one of the panels and scroll down to the link for installation instructions. You may find some useful info there. I think in general you want a slope equal to your latitude, give or take. I have a neighbor who did what you are suggesting and doesn't seem to have issues. I suppose there aren't any warrantee issues. So it looks like you will be facing north-east. It probably wont extend you season as much as would be possible. What about placement on the detached garage? I think drainback is really a concern with freezing - which can happen.