We are looking to convert a flat roof to a peaked roof on a 1312 ft2 house built in the early 60's (see picture below). What is the best way (method) and most cost effective way to achieve this? This will be the first in a series of renovations for this home we want to move into about 2019.
You can build the new roof system right over the existing and once it is watertight you can remove the old roof or keep it as a storage space (attic). You would have to build gables and rafters to be able to utilize the space, pre-made trusses would take away usable space.
How are you going to remove the old roof when you build framing over the top of it?
Why would you want to remove the old roof in this situation?
The OP needs an Architect not a roofer.