If your house has a flat roof, it is easy to walk around
Check Metal Flashing, Patches, and Collars on Plumbing Vents
Let the roof completely dry for several days. Get on the roof and remove all debris and note cracks, missing sheath pieces, and areas where tree limbs could tear material.
Examine the metal flashing for cracks, peeling, or tears. Metal flashing joins the roof to other parts of the building like plumbing vents, chimneys, or skylights. Metal flashing commonly has two layers: step flashing or an interior layer which connects to the parts and a protective counter layer. These layers must expand and contract to protect the roof.
Check the collar around plumbing vents. There should be a flange in the collar that covers the opening of the roof. Also look for spots where someone may have tried to patch the roof with tar or caulking. Patching will be obvious in areas that look different from the rest of the roof.
Look for Seams and Low Spots
A seam on a the roof is commonly prone to leaks and deterioration over time even with a tight seal. Check the seams with your fingers to make certain the seal is secure and void of cracks. Low spots form on flat roofs from pools of water after the roof dries indicated by rings. These rings often get smaller as they get to the lowest point. Look in the center of the rings for holes and cracks.
Do the Hose Test
Try the hose test. Get someone to be inside the house so they can tell when a leak is spotted to keep you from climbing the ladder too much.
Remember to be safe when you walk around on the roof looking for leaks and climbing ladders. With some work, you should be able to detect a flat roof leak. If you can't find it or don't want to wait until he rain stops, you will need a roofing