Portal Frame Extension

[Renovation]

My 8mx8m extension is using a portal steel frame as it has a wall of glass.

A local structural engineer has done the calcs and specified a 6"x4" I section which has a haunch at ceiling level but not at the ridge (as I want a vaulted ceiling)

However I have approached three fabricators and they all say that in their experience it's too small and requires the ridge haunch - every one has said this and one even called the Engineer directly as he was so concerned.

I'd rather not pay for a second Engineer to check the first's work (nor wait weeks for the results) but I am concerned as I tend to respect experience over a page full of numbers - is there another option (other than build it, then sue when it fails).

Would / could the Building Inspector check it ?

[Renovation]

He tells me that it is fine but that he can specify larger sections and ridge haunch if I want.

But I don't want bigger / heavier details if I don't need them.