Building a mason bee house is as simple as drilling a bunch of holes into a block of wood (make sure the wood is not pressure treated or does not have chemicals added), adding a small piece of metal to the roof to prevent excessive moisture and rotting of the wood. Hole size is 5/16th of an inch and about 3/4 of an inch between holes, I have seen other designs with different size holes and with closer spacing.
An interesting fact is that honey bees are not native to North America they were brought to this country by European settlers. Mason bees are native and do very well in North America. Another interesting fact is that mason bees are more effective pollinators than honey bees, the average mason bee can visit on average 1,000 flowers in a day where a honey bee visits only about 400-500 flowers in a day.