This is were I think you will have problems. The bottem cord is what hold the roof all togeather, and if you move it up on the top cord your defeating the purpose of the truss. Did you know that the bottem chod is what helps hold the walls from bowing out. If you look at old garages that have the roof caving in, it's do to the walls spreading out. What i suggest is to do what my brother-in-law did remove the roof, add a 2'-3' knee wall on top of the walls then rebuild the roof.