need someone to make a scenario or teach me how

I want a scenario that takes place just before the Roman invasion of Britain and goes until say 500 ad or later. I want as many tribes (if not all) in Britain, Ireland and Northern Europe as possible. Id like it to be a very large map with room for plenty of cities. Id like most of the map to be about Britain and Ireland with the northern coast of Europe until Denmark and a chunk of Norway. Id like to keep scientific advancement as realistic as possible as well. Can I get all of the tribes to be playable? One last thing Id like the Roman territory to be advanced to its location prior to invasion. Anyone care to undertake this?