FIRST provides building instructions for a wooden table, but here are some portable options. Note that the closer your table is to the specs, the better your experience will be at a competition. Therefore, building a table out of alternate materials (foam board, corrugated plastic, metal, etc.) can impact the operation of your robot.
The following discussion is based on conversations in the Facebook Group FLL: Share & Learn.
Official build instructions
FIRST Build Instructions
. Please note that the location of the Challenge mat on this table varies year-to-year. You will need to consult the most recent Challenge Release Documents/Robot Game Rulebook for mat positions.
Portable/Folding table designs
Portable table for purchase
There may be other options such as “corrugated plastic”. However, the AndyMark table is the closest for-purchase table to an actual wooden competition table. The closer your table is to the specs, the better your experience will be at a competition.