Structural Drawings and Calculations

We are seeking someone who can assist with a used building that we have on site outside of Royal Wootton Bassett (currently dismantled). We have images of the structure when it was erected, but no drawings/specifications other than an overall size. From what I understand we require;

Our immediate Issues -

1. The building will not be long enough for our requirements and therefore we would require additional rafters, braces, eave beams and columns to be fabricated, but the companies that we have approached all require drawings prior to either quoting or fabricating.

2. The building loadings for the type of roof that we would prefer, the purlin spacing to achieve this and whether we could extend the length of the purlins to achieve longer bays.

3. Other than the rafters, there are no braces, eave beams or purlins. The columns are 6m steels and would require plates to be welded on.

I have attached (my) very crewed drawing of the rafters and columns, of which there are 9 sets., along with an image of the building when it was up.

I have quite a few questions over the building and what we can and cannot do to it in order to achieve the structure that we are after but do not wish to bombard you with these here. Is this something that you would be able to assist us with