Wait...Where does one get those sideways rounds?
What I do is export bricks from a program called Leocad, similar to LDraw, into Google Sketchup and trace around the bricks with it to get the right shape for the brick I need, then delete the imported brick as it's dirty (meaning excessive polygons, triangles etc) and add the color and BL brick nub texture to the traced brick after finishing it up, building a brick to use in the model. Then, I do the same thing for each brick I need for the model I'm building (I keep a large save file that has all the bricks I have created in one place so I only have to create them once), then I build the vehicle like you would in BL or IRL. I then check all the textures on the bricks and stuff to make sure they look good and nothing is reversed (it happens more often then not) and then export it from Sketchup as a DirectX, or .X file to Milkshape, where the shading, attachment points etc are done and then from there it becomes a DTS model. Needless to say, what I do requires a pretty good knowledge of how to work Sketchup and is not something you learn instantly.
They are custom made. Guys, in case you missed it these are fully functional, drivable vehicles, not just bricks. How I made them is here, from my brick vehicle topic:
This is just fantastically epic. It's made out of bricks and has a cool structure!10/10
I really like them all, though I don't like that space logo on it. Kind of ruins it. Still, nice job.