or what do you plan on using this area for, living space or just a lot of storage ????
depending on the intended use of the attic space. you generally will need to add larger 2x boards like at least 2x8 or may even 2x12s to the 2x3s that exist. each new boards should be sistered to the existing 2x3 and and they need to span the full width of the space across the two load bearing walls. if you plan to use for living space consult a structural engineer or architect to be precise. otherwise you can be ultra conservative and go with 2x10s or 2x12, but willl cost you more in materials. good luck LJ