If you have never built one, try a simple hypothetical to start. If you have never used the map editor the advanced one that is activated with the purchase of the extended edition is very powerful and allows you to cut sections from an existing map and paste them into a new one.
Experiment with a smaller existing scenario
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"You are never to old to rock and roll if you are too young to die".--- What do you expect to be doing when you are 80?
Hi. I've been meaning to do this as well to 'port' all those fine scenarios found in the SPWAW community, but AFAIK the only way to do it is thru "Eyeball 1.0", the same way I did convert stock and custom scenarios for SP1 and still plan to do more as well in the future.