Most people already have an idea of what kind of a house they want by this stage, whether it is a single storey bungalow, a two storey house or a dormer. This is when you have to find out if your plans are feasible or whether you have to revise and rearrange a few things.
You need help from a professional like an architect or an engineer who are qualified and certified in this matter to give you advice on what is possible and what is not. They would also be able to tell you if your design would be acceptable as far as the Planning Permission is required. For example, if you are planning to build a two storey house in an area where it is established with single storey houses you will not be given the permission, so before you waste your time and money on doing the design and the drawings get advice on this matter.
And it is very important at this stage to talk to your local planning engineer and get their advice and recommendation about your build. Remember, do not walk in demanding that they should comply with what you want and expect them to sit there and agree with you on everything, at the end of the day they know the area better than you and they have to make a decision as far as what is right or wrong and what effect it would have on the environment, they have the final say on whether you are going to get the planning permission or not, so do listen to them .
When you are designing your house do take a few things into consideration, for example ,
Are you going to have services available to the site or do you have to arrange for your own supply.