Hi, this is my first thread

. Excuse me for my bad english but i don't speak english very well.
I would realize a large Diorama with many ships. I buying the 3d models of ship and i attending confirm from the vendor.
It will be in scale 1cm=1km because i want include the Ark Mechanicus Speranza and the Gloriana class.
I still don't know which Gloriana to include, the other ships will be Retribution Classes and Mars and Overlord cruisers.
For the Chaos faction I would like to include the Vengeful Spirit from Abadon, the planet killer and other support ships I am still undecided about. I already know that it will take a long time to print all the 3D models but it will be worth it.
My doubts concern the colors to be used for Hope (since there are no canon photos) and dimensions, Ark Speranza is described as being as long as a continent (in the novel, so this is the canon parameter), but some on different forum credit it about 150 km. On reddit a user deduced the dimensions by extrapolating them from the dimensions of the ship's interior and the external parts described and came to the conclusion that it was long between 350 and 1100 km.
So I ask you that you are
40k veterans unlike me, how long is the Ark Hope actually?