You will need an architect to plan and draw out the plans for submission to your local council for approval prior to beginning work.

This is to ensure the safety of your building and that the right specifications are used towards your renovation. This would be the time you can choose the overall outer look of your house and its inner lay-out.

It's a time consuming process so be prepared to wait. Chances are the plans will have to be submitted a few times depending on feedback before approval is finally given.

Hope that helps.