The exact vessel you want modelled. Name often isn’t enough since many ships have the same name. If you know the year it was constructed or any other identifying information please include it.
How big would you like it to be? If there is a certain space you want to put a ship model, I will choose a scale to make the model fit. If you want it to a specific scale (maybe you have other models to the same scale) I can tell you how big the finished model will be.
Do you have any documentation? If you have photos or plans or anything else describing your vessel that helps a lot. I have sources to get information, but the more documentation I have the better the model will be.
How would you like it displayed? Am I providing an acrylic dust-case or just a base to set it on a surface?
What are you doing with the model? Is this to be a museum piece? A ship-builder’s model? Everything I make is up to a very high-standard and I don’t generally build simple decorative models, but it does help to know where a model will end up being viewed.