When to have a new roof installed on my house?

patch the roof and make it weather tight for the winter. In the spring (lowest temp 50 F.) re-roof. If you have 2 layers now, strip it and then roof it. Make sure they apply "ice and water shield" at the bottom and in the valleys. Check the codes with your area building department and don't allow the roofers to take any short cuts. (a permit with an after job inspection is advisable)