Planning permission this can sometimes be done for you already if you property and it is advertised that it has approval you will not require this. If you own a property that does not have this on it, you will need professional help. Architects can be invaluable here or someone who is a property developer themselves or a property developing company offering Project management can help. Using a professional can take the pain and stress away from you making it a much better experience.
Finance is one of the most fun topics to deal with. As we all know talking to banks can be difficult to get finance for homes. And the same if not more difficult for projects and a good financial package is required as all banks will have requirements including profit margin. Banks will not lend on a project with a lower than 20% profit margin.
Deal Making Decision Point
Examples of bad Planning and Design
Planning Starts Early
And do not forget to have an exit strategy at all phases!