There are WarHammer mods including Dark Elves but if you still want to...
Look at my Tiny Nation mod
http://www.dom3minions.com/files/TinyNation.dm
If that seems fairly clear and you still want to then I would suggest grabbing a larger more-involved mod and look at the .dm file for that. Read the modding manual that came with the game. Take a stab at making a mod then come back with specific questions
If you really really are determined to make a large mod then you might want to ask on the Dom3Mods forum at
http://http://z7.invisionfree.com/Dom3mods