There are a few important things that you should do before you start your building process:
1 - Do your homework and cover any objections or problems that might arise during the build. Always have a back up plan in case you need it.
2 - Get everything in order and do a timetable, but be reasonable as things do not always go as planned, especially the weather.
3 - Make sure that you have taken all the proper precautions as far as Insurance and health & safety are concerned.
4 - It is very important that you have a written contract with all your contractors, detailing what is required and the quality of the materials that is to be used.
5 - When you do your budget, add an extra 20% to cover unforeseen circumstances.
6 - Stay calm and do not panic if things do not go as planned, there is always a solution, you just have to find it by looking at your options.
7 - Get involved as much as you can, even if it is just overlooking the project from time to time. It is always a pleasure to see a building and project progress.
Source: Irish Association of Self Builders 2011