Our home is 2x4 construction one story 6/12 pitch. The plan is to add a 12x28 room in the attic which is above three BRs, hallway, and 2 baths. A 12 x 28 br and closet, 12x28 hallway bath and br, and a 16x28 mr br bath & closet. This part of the house is 28 X 40 above a crawl space. The other part of the house sets on a basement. I will be adding 28' lvl beams in the crawl space under the the walls of the 12x28 hallway bath and br which is approx in the center blocked solid to the foundation. The attic room will have a 5' knee wall on the south and a 7' knee wall on the north. The west end of the room will have a window and the east end will have a door to the stairs. The stairs to the attic will be above the stairs to the basement. I plan to use 2x10 12' floor joists 16" oc and build a frame out of 2x4 for the knee wall and 2x8 up the slant (room for insulation and air to roof) of the roof to the collar ties. Not sure about height of ceiling. The roof is supported by 2x4 40' double fink trusses 24" oc. I have been advised to laminate each truss with 4x8' 1/2" plywood and a truss manufacture indicated that building a frame with 2x10 floor joists with 2x4 & 2x8 framing was enough. Any comments or suggestions would be appreciated.