I actually have several plastic ladders from Games WorkShop WFB Siege Tower, but they weren't long enough. I also thought they were a bit narrow, so I gathered up some square wood stock. The uprights are 1/8" square, while the rungs are 1/16" toothpicks. I cut the uprights to fit the model, then played around with different arrangements until I found one I liked. I felt 20mm between the rails, and 10mm between the rungs looked best. To keep the uprights parallel, two angle squares were taped down, spaced for the 20mm width. You can see the faint pencil marks to locate the rungs, which are 30mm long, and were cut with the chopper I made. I used carpenter's yellow glue to hold them on. I had planned on drilling each intersection to hold a small brass nail for extra strength, but I just couldn't see putting in another 30 minutes. I might poke a hole in each location, then stain it with a Sharpie, to simulate the nail holes.
The finished ladders. The two long ones attach to the rear of both sides, allowing access to the upper rear platform, as well as both gangways. I doubled up the bottom rung, as the ladder hangs out in space. (You'll see in the next shot.) The short one goes from the right gangway to the upper front platform. As you can plainly see, the pencil marks were merely......suggestions.
The ladders in place. They were glued directly to the ram's framework with the carpenter's glue.
I'll try to get more done today. Thanks for looking. Don