Prefab garage trusts

No idea where to start with this one, purchased my first property and I'm looking to sort the old prefab garage out, it's got a flat roof with holes so the sheets will be getting replaced but whilst I'm in the process I want to make it pitched for a bit of extra storage. I was looking for recommendations of where to purchased the metal trusses from and ideas for prices as I'm clueless and pointers appreciated.

Ta