1200 Skaven

With that number of guys, any army will have a difficult time with it as they're likely to be vastly outnumbered. Nonetheless, your units aren't fantastic in CC, but they do have excellent durability due to strength in numbers. To reinforce this, I think I'd try to add a battle standard bearer just to ensure that your guys stick around.

Your warplightning cannons can be really scary assuming you roll well. :P To add in more to the randomness and to better help your shooting efforts, why not try to fit in some weapons teams. I don't play Skaven, but I think you can attach them to your clan rats and storm vermin units. To do this, I think you should look at your slave units. I know each unit is only about 50 points, so see what you're afforded by merging two smaller units into one bigger unit, but with fewer guys altogether.

As I mentioned, I don't play skaven, but have played against them quite a bit. Getting stuck in with them is frustrating when they just won't run due to steadfast and strength in numbers. As such, I think adding a bit more shooting to help whittle down your opponent, while adding a bsb to ensure you stick around would really help make a more consistent strategy. :)