I am building a room inside a garage bay. The room needs to be 18' wide on the inside. The length dimension will be 18'-29', still undecided about how much room I require. I will be using OSB I-Beams for joist (?silent floor joist?). I need to know what width of I-beam will be required to span the 18'. The ceiling load will be 5/8" sheetrock, the I-beams (of course) and 3/4" plywood. There will be light duty storage on top of this, no more than 20lbs/sq ft. and probably a lot less. This will be on a concrete floor and probably 2 x 4 construction, possibly metal stud. Thank You.