Hey! Bit of an open question really because the amount of choices for skaven is HUGE.
Off the bat i love the following things in my skaven army:
Rat ogres
Hell pit abomination
Grey Seer (especially plague magic!)
War machines are so fun! (personally dnt like weapon teams but love Warp cannons, but thats just me, everyone is different)
Plague Furnace (Again this is my personal love and i dnt like screaming bell but many people would argue that both rock)
Deathmaster Skitch (or w.e hes called!)
I started my army by buying the skaven bit of island of blood online 3 times.
I always start my list with 3 units of 40+ and then make the most characterful, fun and competitive army i can!
Bit of a info vomit there but you were very open with question so i hope that kinda helps!
Good luck with building your own version of the most mental army in the game!