Just starting out - havent gotten a 3D printer just yet, but learning a ton from others who are posting - so huge thanks to 3DBotmaker and all the other content creators!
My 3 year old son just loves watching all of the racing videos (yes, he's the only the one that loves them ;) ) - he got a huge kick when I made a few pieces of track from Coroplast for him - just starting out simple enough with straights connected with Kinex (thanks @Phil) - I then wanted to to do a curve, but without a 3D printer - turned out to be much easier than I thought:
The base was ~18*24 - each wall is ~1 inch high that i screwed into the base from underneath:
I used #6 3/8 screws - thin enough to go through the edge of the wall, but not long enough to through the top end - I first laid the curve out where I wanted it on the base, then with my drill screwed through the wall and base to make sure it was all lined up well enough
Not crazy sophisticated yet by any means - but thought this may be helpful to others who may just be starting out