Oh that's a good idea!

Before, during and after you build you are always learning, here a just a few things that might seem obvious but you may not have considered.

Don't be in a rush to get the build started, the more time you spend at design stage, altering and changing designs and sizes of rooms, were walls will be even down to where the plug sockets will be will result in time and importantly money saved on site. The less decisions to be made once the build has started the faster your builder can get on. Time wasted on site is costly to the bank balance.

If you can recycle it or do it yourself then do it. Does your site have buildings/walls to be demolished? A few hours or so of hard labour, sweat and tears and you can get that building down, may be recycle the bricks for walls that wont be seen, crush it for hard core or even sell, the works is hard but the savings can be large.

Buy all or as much of the actual materials for your build yourself. With a detailed specification and programme you will know exactly what is needed and when. Shop around, shop around early, look for sales and bargains, your builder will only buy from his easiest and not necessarily best priced supplier and will even add his own profit. This then leads to ensure you consider secure storage for materials and will they be accessed in the order they are required if the site is small. 

Never get just once quote. Always check your quote includes for everything you asked for and you comparing like for like. Read the small print carefully and ask if you are unsure. Learn the art of haggling, if you don't ask you don't get a little bit more knocked off your bill. 

If this build is not your forever home it is also worthwhile considering the type of people who will buy from you at design stage, design in your requirements but also consider others requirements too, don't design resale cost out of your build. 

Remember to keep your tradesman on your side, a happy, inspired team will always be happy to help when problems arise and importantly work to your schedule the best they can. They can also be the best place to find the right advice, they have the experience and the vision of the end result and will know if your idea will work.

Keep up to date with the paperwork, it may be the most boring part of the project but you can only claim your VAT back once on a new self build and you need to be claiming as much back as possible.