Hi
@Rusty01 and welcome to the forum. The main/usual problem of water causing damage inside is because the sealing on roof between flat surface and roof ridge has hairline cracks caused by improper/insufficient use of sealant and/or weather damage from extended exposure to hot/cold sun. Also if you have any other attachments to roof, a/c, roof racks, solar panels, television antenna, the sealing there too is subject to the same break down caused by weather conditions. To reduce pooling on roof, you will have to have greater slope to allow water to run off and not build up behind the higher outer ridge of roof. You then only have to worry about the lower end being in good condition.