Create Opening for folding doors

Hi All

I'm looking at sourcing some folding doors 3015mm and 2836mm. I need to create the openings for these by extending an existing door opening and also extending an existing window opening these openings are going into an existing one storey extension.

Could Catnic(?) lintels do this job or would I need RSJ's. anyone able to supply a rough price for some one to do these opening and a rough timeline?

I'll possibly get a SE to look at this and advise on the openings and agree what needs to be done with door supplier, I'd just like a rough idea of what creating the openings would cost.

Thanks in advance guys.