Well I wouldn't purport myself to be the skaven master tactician, but I have played them quite a few times. Warp Lightning Cannon, Hellpit Abomination, Doomwheel are all amazing. You really want probably 4 pieces chosen from those 3 items minimum I think. Alot of people do run stormvermin, but I don't know if I can say how much they are worth their points relative to other options. You want a minimum of 2 x slave blocks of 40-50 slaves, probably 3 honestly.