I've created a table for all the little robots featured on instructables to drive around on.
It has the height of a standard coffee table and is constructed from very basic and cheap materials.
The table has an elevated edge of 50mm to ensure that the bots don't fall off the surface.

For some examples of robots this table can handle you can check out the following links:
Bristle bots: https://www.instructables.com/id/No-Solder-Funny-Robot-in-Minutes/
Drunken drawing robots: https://www.instructables.com/id/Drunken-drawing-robot-/
Vibrobot: http://boingboing.net/videos/vibrobot.mov

To make your own you need the following:
materials:
- wooden panels (OSB)
- small scews
- metal corner fasteners

tools:
- (electric) screwdriver
- table saw (or order the OSB panels with specific dimensions)

Step 1: Your Tools

Step 2: Materials and Measurements

Collect your materials and mark the wood in such a way you can do all the cutting at once.
For my table I've used the following dimensions:

1x 764x764mm (table surface)
2x 420x764mm (inner sides)
2x 420x800mm (outer sides)

These measurements deliver a square table with an outer dimension of 800x800mm.

Step 3: Cutting Up the Wooden Panels

Use your markings to guide the sawing process.
If you're using the table saw I would advise you to get some assistance, since it's one of the most dangerous machines in any decent workshop.
Don't forget to pay attention to which side of the line you're supposed to cut.

Step 4: Assembling the Panels

Screw the panels together using metal corner fasteners.
For extra stability you could apply some wood glue and some nails put in from the outside.

Step 5: Attaching the Table Surface

Attach the table surface in the same way as described in the previous steps.
Make sure that the surface is lower than the edges of the sides, so that the robots won't be able to drive off that cliff.
The photo shows the table bottom-up.