Whe we did one I based it on the example on the AWGB web site, you will need to adpt it to your own situation.
I did one for the AWGB 30 Birthday Bash, when we had a stall in the local park, the council sent me an example, they used the Christmas Market where they expect 120,000 (yes that is one hundred and twenty thousand!) people over three days, just a bit over the top.
Ron