Advise on where to begin a sunroom

Hi,

I am starting a bungalow renovation soon.

part of this will include a new sunroom extension.

I know what I want and will be able to supply details of dimensions and a 3d model of how I want it to look.

Essentially it'll be 3 glazed walls with an open gable on the new end. This will be be perpendicular to the old roof and will intersect the old roof whh 2 valleys (hope that makes sense)

Something like this ( https://imgur.com/O2UkZxx ) but where the new roof meets the old will be different obviously

There will be no block work to support the roof above

So my question is, where do I start with structural design?

I don't believe I need an architect as I know what I want and its under planning permission size requirements, do I need a structural engineer to specify structural steel? Or should a builder be able to do all this?