How much slop is needed in a 12x10 foot flat roof
adding on to side of garage
Confirm minimum slope is 1/4" per foot but locale is a factor. If snowfall is a factor the minimum slope should be at 4:12 or 4" rise for every 12" and roof framing should be adjusted also.
General rule is 1/4 inch per foot. So, if the edge your roof is going to be 10 feet from your garage wall the slope should be 2 1/2 inches.