Right, some info on the portal frame. Dad sourced it from Wareings, who are a company based in Lancashire -
http://www.wareingbuildings.co.uk. Apparently they weren't the cheapest around but matched what was wanted the best at the time. The kit was about £6,900 (ordered about 3-4 years ago so prices aren't current) and included the insulated roof sheeting and the guttering, as well as the four roof light panels which were extras.
Foundation requirements will depend on local building control and the site, as well as what you want to do regarding cladding. The frame will need a minimum 1 cubic metre pad for each leg of the portal, so 6 in total. As we were building traditional block walls into the structure and had wet clay soil combined with the usual jobsworth building inspectors, we had big trench foundations and poured a total of about 50 cubic metres into the foundations and floor (for a 36'x30' structure). Then you just need to add in the cost of whatever method of enclosing the structure you want to use - wood/metal/block.
Because planning say no more than 30m square of floor without permission, any more then 10 square meters and you need building regulations to be involved.
Regarding planning permission, I'm fairly sure the information you have about size is wrong. With regard to outbuildings, the following restrictions apply for permitted development (assuming you're not in a listed building or on designated land such as an area of outstanding national beauty):
* Cannot be forward of the principle elevation
* Total area of all outbuildings since 1948 cannot exceed 50% of the grounds of the property
* No living accomodation or TV antenna
* Max eaves height of 2.5m and overall height of 4m for a double pitched roof, or 3m max otherwise
* Any part of the building must not exceed 2.5m in height if any part of the building is within 2m of a boundary
If all the above criteria are met, then what you are proposing is
permitted development and does
not require planning permission. If the structure is over 30 square metres in size, then you have to comply with building regulations - but planning should not be an issue.
Hope this helps.