It's widest part is about 105mm. If you make the arch 120mm x 80 (width x height) It would be a good fit. I measured this off my model, but a good tip, if you dont have the model and just want rough measurements, copy the image off the GW website, paste it in word and size it (locking ratio aspects) until the base is the right base size for that model, then measure off your screen. This is rough and not perfect, but has worked for me to make terrain pieces while waiting for my models. Hope this helps
