Before you begin, consider a few low pitch roof installation basics. A low pitch roof offers more challenges to roofers than a roof with a steeper slope, or pitch. A low pitch roof can be installed directly over the old roofing, but it has some requirements on how much slope is required.
Inspect the Roof Sheeting
Be certain that the underlying plywood is in good condition. If there are places that have rotted from old leaks, tear out and replace that section. Simply covering up a bad section of the roof will not solve the problem, and leaks will recur at that spot as it continues to sag.
Remove All Nails and Debris
Make sure that there are no protruding nails, screws, or other debris. If your roofing material is not able to lay flat against the top of the house, its seal has been compromised, and leaks are likely. Old screws and nails are notorious for puncturing shingles and rolled roofing, and are easy to miss on a cursory inspection.
Plan Ahead and Save Time
Plan ahead, and have all of the required materials on hand before you start. Having to stop work to pick up additional supplies could result in rainfall before the job is complete. Make a checklist before you begin, and pick up everything you need at one time.