What should I budget for a single storey extension measuring 6m x 3m approx, with a flat roof and single rooflight (the extension needs to be 2m above ground due to dropped garden)

because of the drop in the garden ,this job will obviosly be a touch more expensive ,for an extension like this and what you have described i would allow 20k to full finish ,

An estimate would be £1200 per square metre. This allows for the fact th you would actually be building 1 1/2 storeys.

Hi your looking at around 18 thousand depending what else you have planned for inside regards brett

hi you sould be budgeting for an average build price of between 1000 to 1200 pounds a sq m for a basic build ,if you want walls altered and a kitchen fitted and fitting then this will go up ,expect to pay extra for raising the level of the extension up to dpc if it is much lower

As a rough estimate I would advise around 1,200 per square meter for the finished extension itself, so roughly 20,000 for the build. It will go up if you want bespoke furniture it it or a kitchen fitted. Also, as a general rule, I would say keep an extra 10-15% as contingency for unforseen costs such as: piled foundations, moving the public sewer, accidentally going into a water main, the cheaper roof light/door not being in stock, that window with built-in blinds that would be great in the new place etc. You would be surprised how not uncommon the above "unforseen" circumstances are.