(Newbie) What kind of object to model a tramway shell for 3D-printing ?

Several years I spent a few evenings playing with Blender, but quickly fotgot about it because , as a railroad modeller, I didn’t see any practical use of that software.
Now , with 3D-printing the situation has changed and I would like to built some engines and wagons shells using that technique.
Here are a few pictures of what I would like to model:

The prototype
my paper version

So, here is my question:
What is the best kind of objets to model the shell of that tramway ( and the open wagon ) ? should I use meshs , curves, surfaces ?



Use Meshes.
Curves can be used to make elements then convert to a mesh
Surfaces in blender are pretty useless for this

Only Mesh for me. You got basic shape in your prototype and round corner are peace of cake. Its possible to model the second picture in one day max if you know blender

I found a pretty nice Tutorial explaining how to prepare your files for 3d printing in blender

The most important thing is to have everything manifold (also called watertight), the select non manifold option is very usefull for this, it just shows you the places where something is wrong.

Thank you Richard, Blademust and Blendfile for taking some of your valuable time to reply. Following your advice I’m using meshes to design the tramway shell.
I checked the Shapeways website a few weeks ago and I remember reading the topic about manifold objects.
Maybe I should start with a simpler project: the low sided wagon on the picture #1.
The shell of the high sided wagon on picture#2 is made out of Plastruct sheet and structural shapes.