Scale is the interesting part of this conversation. I have custom made walls to properly fit the 40x20mm stands 2 deep for the attackers and the defenders to be fighting on the wall. There fore I had to make sure to make my own siege towers to perfectly fit an entire unit's 3 stands on the wall and tower, I just don't know how to do a representation of the sally gate, the rock piles and the boiling oil. I found a magister militum that makes some nice looking models (I don't own any and I am just looking at their website pictures). But I was thinking on just flocking a dime size base with rocks to act as a token for rock droppers. Rock droppers being the handful of guys that are assigned to pick up the rocks and dropping them onto the attackers

I have ladders and mantlets, I could make some log rams but I know those would end up looking like poo
and I could make the sow's much like the battering rams but I have yet to even want them in battle

I found some earthworks on pico armor that I think would work great ( have not bought them yet) They have some bunkers that could possibly work for artillery bunkers and both kallistra and the magister militum have siege cannon units that would work perfectly for mangonels, bombards and tribocks. Both sites also seem to have the same palisade walls, mantlets and....I forget their name now....privos? not a mantlet but a large shield.
I have attached a few pictures of my game. The cannons on the tower took out 1 siege tower and 1 battering ram on approach, the second tower was brushed off by the defenders but the third battering ram took out the gate exactly the same time the chaos warriors took the opposite wall by ladders (with miracle rolls, actually killed a stand of rangers in the process).
Oh, there is a random 2 story house out in front of the walls in one pic, ignore that thing, I don't know what it's doing there.
I am getting my list together and then making one large purchase across all of the web.