Made these this weekend for the bees. Pretty easy project, and a big thanks to Surferguy, who I turned to for finishing ideas. He suggested a few options, but caught my attention with the one that uses fire. Shiggy...shiggu...shig something Japanese. I burned them lightly, then scraped with a wire brush and gave the cedar a heavy coating of mineral oil.
The most expensive and sucky-est part is finding and cutting the bamboo. Home Depot had the right size(many are too skinny). To cut them I left them in their bundles of 6 and used the chop saw, which mostly works well. The interior blocks were from an old bee home we had bought that fell apart.
These came probably bigger than I needed(and took lots of bamboo). The exterior cuts are 6 inches, I think 4" would be perfect. So I'm going to make a couple that size for my nieces for Christmas.