Well checking out "the Legions of the Dead" is a good place to start. It will give you ideas on how other people build their lists and hopefully give you some ideas. Also, if you haven't got it yet, grab the army book.
If I were going with a Lahmian themed list I'd go for Female Vampires, Coven Thrones, skeleton warriors mixed with Tomb King skeleton parts, Grave Guard with Tomb Guard weapons etc. If you go for an undead legions list you can even include TK units like skeleton archers, skeleton horsemen and the like, all adding to the Lahmian theme. You can even get the queen of the silver pinnacle herself, Neferata, The Mortarch of Blood.
Looking forward to seeing your take on it.
