It's rather dangerous to give out plans, without knowing any specifics. Some structural engineering should be done to calculate the loads, and size the beams, particularly if you're putting in a large loft. You could have a serious structural failure and possibly a very hazardous collapse (which is bad).
There are some lightweight wire shelving systems that can be installed. Keep the weight down and you won't have an overloading issue.
There are some lightweight wire shelving systems that can be installed. Keep the weight down and you won't have an overloading issue.