I'm an ex Civil Engineer and at one time, part of my job was checking calculations and drawings submitted to the local council for planning permission approval. There are several ways of doing a loft conversion and usually you only need to RSJ's (or similar), but sometimes you might need more (although 6 seems a lot). Depends on size of conversion, load bearing wall layout, proposed loading, deflection of beams etc. Your best bet, if you are not happy, is to go to a consulting/structural engineer (or even the original architect) and ask why there is so much steelwork in the design. It would be impossible for any to say on this site without seeing the drawings etc.