There are a ton of free content sites for WoW already. What value would your service add?
sites like
thottbot wowhead wowguru (just to name a few) have tons of information and guides already.
there is also a wow wikipedia
wowwiki that is 100% free user generated
most these sites make money off ads, not many use adsense tho
what kind of information would your site have would make people want to pay to be a member of?