Structural engineer for loft calculations

The house has 2 rooms in the top floor. My builder has stripped them out, and I would like to open the rooms up to one large space with a vaulted ceiling (the ridge ht is approx 3.8 metres from floor) and a large dormer to the rear. I would like to look at raised tie trusses if feasible. . I have attached photos of the before and after strip out and can provide architectural drawings too if required.