Garden Wall Construction Recommendations For A Garden Office Supplier/builder? South East England

Recommendations for a garden office supplier/builder? South East England - garden wall construction

I need a garden office made, probably a sort of wooden hut, but I'm open to other species.

Due to limitations identified (area as an area of outstanding natural beauty) I need a building permit for themselves and need compatible with forest trees (environment).

You must be at least 20'x12 '(6m x 4m), does anyone recommendations of the suppliers and manufacturers of these buildings?

Search all pages and on eBay, theres all kinds of different thickness of the walls, ceiling beams, roof structures, etc. - who knows a good site I can find more information about "information on the technical aspects of this type of building?

I have very large files, and other pills, must go, the more secure and should be isolated, and the electrical system, etc. - Does anyone have any hints or tips to help you in this regard?

My budget is around £ 10k.

Thank you all!

Jim