Top down is good. gives a basic structure. An organization scheme like Balthasar's proposal is really describing a portal or a set of portals. a "Modding Units" portal would include a link to the article discussing terrain effects on units just as a "Modding Terrain" portal would. But each would link to many articles the other portal did not.
The other important part of building a wiki is writing short articles that can later be expanded & that hopefully include links to other parts of the wiki. Portals don't do much good without articles.
Take terrain & maps, for example. Having combed through many threads, I've re-organized pieces of the various discussions about maps/terrain into blocks of related text. I'm now redacting those into articles on the following topics:
- Map Design Philosophy
- Using BMP2BIC
- Making Maps From Scratch
- Editing/Adapting Existing Maps
- Using Map Tweaker
- Working with Terrain (includes explanations of terrain files & their interactions)
- Landmark Terrain
- Creating Custom Terrain Graphics
- Hexediting Terrain Types
- Resources
- Controlling Unit Movement
Each of these articles will be shorter & clearer by linking to the articles on related subjects. It's a web, not a hierarchy. Fundamental to understanding a wiki is really getting the concept that anybody can edit anything. I don't expect to post finished articles. Can't since people will later add links to articles that don't yet exist, correct errors, insert sections on newly discovered techniques, etc.
No outline is going to survive without changing either. The schema tends to arise organically as people add & refine articles, make links, etc.
I think one good way to get things rolling would be for each interested person to make a wiki article that is just a stub - the basic answer you find yourself giving over & over again. A simple paragraph explaining palette indexes for example. Then the next time someone asks the same question, just post the link. Eventually more detailed explanations, graphic examples, exceptions to the rules, etc. would get added to the brief paragraph that the article started as.
At this point we need paragraphs more than lists. If anyone is willing to do the basic writing of a short article but doesn't want to get into the wikifying (page formating code, links, etc.) I'd be glad to do that side of it.