So almost everytime I make a cake the cake board is right about the exact size of the cake. However than it makes it hard to frost the cake in an even layer of buttercream. Do you think I should buy cake boards that is an extra 1/8" or 1/4" bigger than the cake I'm baking? What do you suggest?

Cake boards come in standard sizes, so I don't think you will be able to buy a board that is only 1/8" or 1/4": bigger than the cake.

When cakes bake they shrink a bit from the size of the pan. An 8" cake should fit perfectly on a 8" board with *just* enough space for the icing, which you take to the edge of the board. Using a bench scraper, you use the edge of the board to guide you to an even amount of icing.

Hmm my cakes don't seem to shrink enough. Is there something in the baking part I could be doing wrong.

Mine shrink just enough that the crumbcoat fits on the same size board.

If I am putting the cake on a presentation board, obviously I use a larger board. If it is going on a stacked cake, I use a masonite board bigger than my cake. I can wash & reuse the masonite boards. More importantly, I don't get the little wobbles that corrugated cardboard sometimes makes.