Saw this on youtube (thanks Bushcraftusa!). Thought it might be interesting, although don't know if you can get aluminium flashing quite as easily in the UK!
http://www.youtube.com/watch?v=o3VvRwhbIXw&list=UUkxQ9AfOmF_-P30sU25Bsog&index=1&feature=plcp
http://www.youtube.com/watch?v=o3VvRwhbIXw&list=UUkxQ9AfOmF_-P30sU25Bsog&index=1&feature=plcp