When you decide to go ahead and purchase a steel shed or garage the usual process is to pay a
deposit so that the engineering for your building can be organised.
If the shed kit supplier reaches into a draw and pulls out a generic copy of your sheds engineering
and hands it to you I personally, would ask for my deposit back and walk away very fast.
Engineering for your shed should be site specific, not pulled out of a folder in a draw. The shed supplier should submit your shed design to their engineers for checking and signing off on and you should be supplied with an Engineering Schedule that applies specifically to your building.
You can then use the engineering drawings and engineering schedule for applying for your complying development application or construction certificate.