im trying to build a roof rack from scratch and want to use the tracks that are already on the roof. I am not sure how exactly where i should start and what to use...any ideas

 

Just build your rack and u bolt it to the factory crossbars .

 

This, but just bear in mind they don't hold all that much weight, you're better off mounting to the gutters. A number of companies sell mounts that you can weld on to your roof rack. Even if you cant weld you should be able to find someone to weld them on for cheap if not free.

There a number of home built roof racks in the fabrication section many of which were built out of pipe to avoid welding. If you need ideas go look through those threads.

 

But... Gutter mounts have disadvantages too. If you get a "basic" rack with 4 feet they can peel your gutters right off if you overload them, or rub them on a tree. If you already have a factory rack you can ditch the plastic xmembers and get steel feet that attach to the factory rails and the new rack or do both.

 

will it hold the weight of a spare tire though???

 

Yes.