Your optimum angle for year-round use is your latitude. For central Pennsylvania, this is about 41 degrees. If you take a piece of plywood and place the 90 degree corner to your left, measure over 1 foot and make a mark. With a protractor centered on this mark, lay out a 41 degree angle going back towards the left. Cut the angle off, and label the 3 angles, 41, 90 and 49 degrees. Place this angle on the solar panel with the 41 degree angle towards the top of the panel and the 49 degree angle towards the bottom. Put a level on the top edge. Center the bubble and you are aligned.
If you are going to adjust the angle for summer and winter, you need two more triangles. A 26-90-64 (summer) and a 56-90-34 (winter). These are 41 degrees minus 15 degrees for summer and 41 degrees plus 15 degrees for winter. (The 41 degree triangle becomes your spring setting.) Construct these in the same way you did the first, laying out the 26 degrees and the 56 degrees from the one foot mark, respectively. Align the panel the same way.
To check your roof for the summer setting put the 26 degree angle towards the top of the roof and the 64 towards the bottom and level. If the lower angle (the 64 degrees) is in contact with the roof when the upper edge is level, you are OK with your current set up. If the upper end (26 degrees) is in contact when level, measure the gap between the lower point and the roof. If your solar panel is 5 feet long, multiply the measurement by 5 and that is how far the lower panel mount must be raised. (This is the reason for setting the exact 1 foot measurement off of the 90 degrees, before laying out the angle.)
If you do need to block up the lower mount, I would give it a little bit of a fudge factor, just to be on the safe side.