One of the better books to learn about Self Build is called Building your Own Home by Murray Armor and David Snell. Its published by Ebury Press. I used this book 5 years ago when I was learning (I have built my own house). However it won't tell you explicitly how to put an extension together - there are many different construction methods. Understanding enough about Building Regulations to put drawings together for Building Regs approval is, I'm afraid, not easy the first time you do it - and for many people they only want to self-build once. So the only practical alternative is to employ an architectural technician to produce your drawings for planning, and he/she will then annotate the planning drawings with extra information required for the building regs submission. In practice I did most of the Building Regs drawings myself, but there were areas like the structural stability of the roof and the thermal calculations that I couldn't tackle myself. It will probably cost you about �750 for the Planning Drawings and say another �1000 for the necessary Building Regs ones, including your professional making the applications and managing the process through Building Control. An architect will offer you the same service, at a higher price. The statutory fees for PP are about �250 and those for BC about �350 - you can't avoid these costs.