Photo by Patriot Construction - General Contracting

As you plan your remodel or addition, design your work so you do not have to change the roofline. Most architectural styles can accommodate remodels or additions without a roof change. This will result in a significant savings in materials and labor. Most of the savings will be achieved by not needing to tear out the existing structure and rebuild the roof. Changes in the roofline, particularly if they affect the pitch of the roof, can create the need to reinforce the walls that bear the weight of the roof, as well as to alter the rainwater drainage system. The less you change, the lower your cost. While the additional cost of changing drainage from the roof may be relatively minor, providing additional structural support to load-bearing walls can quickly become a major element in the cost of your addition or remodel.

If you found this tip helpful, you might also want to read these articles:
Eliminate or reduce the size of eaves
Use vented insulated roofing panels to create a cathedral ceiling
Use factory built roof trusses instead of site-built rafter systems for your roof