There are a number of different ideas for creating one's own math board game, such as starting from scratch, adapting the rules or game play of an existing board game, or else simply using the board from an existing game and reinventing the rules from scratch. Some things to keep in mind are the skill levels and educational needs of participants, the duration of game play, the extent to which the game is based on either strategy or chance and, of course, how enjoyable it is for the participants.
Existing game boards that can be re-purposed for teaching math include "Ludo," "Snakes and Ladders" and "Checkers." A good example of a math board game using the "Snakes and Ladders" board is "Operation Snakes and Ladders," in which players roll two dice and choose whether to multiply their results, divide them, add the two numbers together or subtract one from the other (with a maximum value for all operations of 20).
An example of an adaptation to an existing game is "Table Fish," which takes the game of "Go Fish" and uses a pack of cards showing multiplication facts instead of a regular pack of playing cards.
If allowing players to create their own game from scratch, it is a good idea to start with a topic or plan and then let them construct a game using provided materials in groups.