I would suggest that you read some other biographies, in particular ones that are of local interest, to see how others have gone about it. If it's a local-interest book, one thing you might think of including is photographs - both of him and the local area - if you have them. Over here (Cotswolds in the UK) we have a lot of local photograph-based books that are popular both with tourists and locals alike. Some of them are purely collections of photographs or postcards, but some of them are historical accounts or biographical accounts.
With regard to structuring, there are lots of ways you can go. The most obvious is a linear narrative - starting from the beginning and having a new chapter for each decade, or each stepping stone (e.g. childhood, first job, marriage, etc.). But you could also structure it in other ways (e.g. section about his work, section about family, section about friendships, etc. or structure it around big local events).
What do you want to get out of the project? What do you want it to say? Where are you going to get the material from (e.g. just your own memories; interviews with friends and family; letters; etc.)? Once you know what your aims are, it might be easier to make a start - either on the research, or on the actual writing.
Good luck!