I am planning to build ceiling storage in garage. One side of it will be hanging from ceiling joist the other one will be attached to the wall. The joist that I am planning to use 20 ft long and consist of two 2x4 linked by metal plate, so it is not strong enough to hold 1,500 lbs of my planned weight. I am planning to reinforce it with i-joist from below and pull and old joist and new i-joist together with giant u-bolts (so ceiling's sheetrock will be sandwiched between current joist and new i-joist). For 20ft width I am planning to use i-joist 14" or 16" tall and have 7 u-bolts. I am curious if this design makes sense and strong enough? I am also concerned about my roof, which might be deformed since current joist is linked to it by 2x4s again by metal plates.
Any thoughts would be greatly appreciated. Hopefully, my explanation makes sense, I am currently learning SketchUp so that I will be able to draw proper illustration.