Jeff, first off welcome to House Repair Talk.
Yes there are materials that are designed to create slope on flat, or areas where water ponds. It comes in either 1/8 or 1/4" increments. Meaning you would have a 1/4" rise in 1 foot. This is called tapered ISO board and comes in 4X4 or 4X8' pieces.
I'd suggest taking off all the old roofing on the flat roof and shingles at least 3 courses on the sloped roof. Draw a chalk line across the roof, length and width to see if you have any swags in the structure. Install the tapered ISO and then install either of GAF "Liberty" Certainteed "Flintlastic" or ABC (if you have an ABC Supply close) Mulehide, base sheet and modified bitumen cap sheet with new drip edge.
This application will last many years. Tapered ISO is not cheap and EPDM carries no MFG warranty on residential applications.