I am making my first wedding cake. It will be 3-tier square. The sizes are 16, 12 & 8 and I found a 20" foil base board but I don't know what size boards to use for the two layers. Do I use round boards or do I cut boards into the same size as the layers? Also, any assembly tips would really be appreciated. Thanks!

I usually cut square boards to size from rectangle or round boards. You would make them the size of each tier.

I go to the framing section of the craft store and get foam board. It is easy to cut into any shape that you need. It is stronger than cardboard, but depending on what thickness you can get, you will still need to make it several layers thick.

Make sure your foil based board is thick enough to support the weight of the whole cake. Depending on how thick your base board is, you may need several layers or may want to consider another base such as covered plywood or something like that. I cut cake boards the same size of each tier, that way it doesn't show once the cake is assembled. Make sure you use some sort of support structure in each tier, like dowels. This is a large cake so make sure support is where it's needed!! There's a tutorial on the front page of this site for stacked cakes, take a look at it and see if it gives you any other helpful tips.

Thank you so much for your advice. I will check out the tuturial. I know I'm probably in way over my head but with some practice I might be okay. The wedding isn't until August so I have some time to figure all of this out. Thanks again.