This guide is a helpful read and will provide inspiration, add unique character to your property and help you take into account aspects of your extension that you may not have already considered before you speak with an architect.
http://www.homebuilding.co.uk/advice/existing-homes/extending/design-guide
This article covers aspects of designing an extension which many people overlook and could be used to transform your home and the way you use it.
Sometimes reconfiguring your existing layout can be as good as, if not better than, adding a traditional extension. To maximise the potential of your home you need to also consider all aspects of alterations, extending up, down and out sideways. The size of each space will have an impact on how you use it, opening up existing ceilings or creating vaulted ceilings with roof lights can create the feeling of much larger, lighter spaces.
Other aspects and/or features to consider touched upon by the article are outdoor rooms, sunrooms, maximising natural light, framed views, privacy glazing, pocket doors, fireplaces, contemporary kitchens, feature staircases, building with oak, noises issues and many more...