What do you need to consider?
Your neighbours
If your extension runs close of to the boundary of yours and your neighbour’s property, you will need to comply with the party wall act.
Before building commences you will need to have a written party wall agreement
Architect
If you require drawings or advice for your extension, you will need to make sure they are done by a registered architect.
Choosing the right architect is very important.
Site access
You will need to factor in site access for trades and deliveries. Make sure there is easy access to the area and space for materials (driveway/garden)