There are a few things that still need to be done like relay the slabs around the edge of the extension but I will do these as and when I find time in coming months.
Looking back, I never really thought that it would take as long as it did even though I was spending significant time on most days - including weekends - on the build. However, I didn't work twelve hours a day!
In general I really enjoyed the build and I was tremendously lucky with the weather in that April was like summer allowing me to get all the foundations, floor slab, walls and roof completed before the bad weather of May, June, Jul and August hit us! I would probably be not so happy if I was held up for weeks because of the weather.
I learnt a lot about building, which was one of the big benefits of undertaking all the work myself. Interestingly, I could not find answers either in books or on the Internet for many of the challenges I faced and I can't praise the local Building Regulations Inspector enough who turned out to be a real help in providing guidance on how to do things. In effect, he acted as a very cheap architect so I would certainly recommend keeping whoever you need to work with on your side.
On reflection, I am pleased to say that there are no major things that I would do differently and I didn't have to do too much remedial work - the door step being one.
I couldn't have undertaken the work without tools and I was pleased that most of the machinery I required I already owned so do not try and save money by not having the right tools or relying on hiring - this could prove to be very expensive indeed.
If you are used to undertaking DIY, are sensible about using tools and willing to take a bit of risk I would advise anyone to have a go. But... Be realistic on the time it will actually take you to complete, especially if you need to hold down a full-time job as well. In that case I would imagine that anyone could become bored with the project extending over twelve months even though you could save quite a lot of money.
Good luck with your own venture and let me know how you get on!