The way I have done it in the past is to create three different models. One I use for the corners, one for the edges, and one for the center. Once you create these three sections, you can duplicate them in different ways to create the final model.

I've attached a sample of what the sections should look like, and how they tile together. I created these pieces by creating a cube, beveling the edges, and created the pegs by cutting some loops into the mesh, arranging them into a quarter circle, then extruding them down. Be aware that the topology I've used is terrible, but it gets the idea across.