Hello , I'm building a 24x24x8 garage, I want to use trusses at a 6/12 pitch ,what will the hight of the roof peek be. And if I want a 1 foot soffit, do I just add 2 foot to the total span of the truss?

6 ft 6"+/- at peak with a 26 ft span. When you have the trusses built, tell them the overhang and they will build it properly. You will want extra gussets at the end so you can bear on the plate. Otherwise, the bearing will be off the wall plate. With a free span of 24' you will most likely need 2×6 construction.

http://i819.photobucket.com/albums/zz111/lacogada/roofhite_zps6f58b1b4.jpg

If you wanted to use the attic space for storage, regular stick frame construction would
Probably be better... as pre-fab truss have so many bracing members, leaves no room.

Also see
https://www.askmehelpdesk.com/construction/what-size-beam-do-span-24-feet-741176.html

With stick construction you will need a girder in the center.
With truss you will not.

Chuck

I agree Chuck.

That's why I included a link to another that shows girder on same size building.

Also see
https://www.askmehelpdesk.com/construction/what-size-beam-do-span-24-feet-741176.html