I think adventure maps are very very hard to get good.
You would need a team of people (storyline, redstoners, and builders) to create a highly polished one that people would like.
I recommend just building something cool.
Baroque palaces are always a good place to start; they are not hard to build and look pretty impressive when completed. (For examples of what I am talking about, there are a 2 baroque buildings on my profile, or check out Kenofox's builds (he's a former Gazamo member, so he knows what he's doin))