Hi I know that it will be different, but i've no idea where to start so in order to give me some idea could you please tell me how much your single story extension cost? Ideally I'd like to extend to create a new kitchen diner, and a wet room. Also, do you need an architect and do you start by calling the architect or a builder? Many thanks!
A (very) rough guide would be between £800 and £1,500 per square metre depending on location, type of construction, amount of work you will do yourself (e.g. tiling, decorating, flooring, etc.) and many other factors.
You do not actually need an Architect especially if the extension is simple in layout and construction. Many builders offer a design & build service. There are also architectural technicians / technologists, plus all sorts of "architectural consultants", architectural designers," "plan drawers" and the like who offer services. BTW none of these are able to call themselves Architects - the title is protected by law.
Obviously, I would advise you consult an Architect (Pendeen's self-preservation finally kicks in here ).
Most firms offer a free or very cheap initial consultation at your home - I have spent many unpaid hours chatting to potential clients drinking endless coffes and scribbling - often without matters progressing much further . Find one here: RIBA