I bought this little mason bee observation hive as a Xmas present to myself (https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1). My garden flowers attract bumbles throughout the season but I have never paid attention to mason bees. This year I might just buy some cocoons at a local nursery store sometime in March.
Cheapest and easiest way I know of to make nesting tubes; cut cane reeds or phragmite reeds of 1/4" to 3/8" inside diameter to about 6 " length, making certain that one end is the closed end at the reed joints. place them tightly into a tin can or wooden box long enough to shelter the tubes. Hang the tubes horizontally onto a wooden fence or a vertical dead log.
Or you can go to the work and expense of building those pretty nest boxes. Or spend a bundle to buy ready-made. The bees don't care what it looks like, but they do prefer older wood, IME.
It is the female orchard bees that do the majority of pollination, in order to get food for larvae. The males only visit flowers to feed themselves to live long enough to mate. Therefore, you want to attract the females. How? With males! If you already have orchard bees in your area, simply having the holes available and appropriate forage and moist soil available should be enough to attract them. Males will come around the holes and leave their pheromone to attract the females.
If you have no orchard bees in your area, you will need to buy them. (many online sources).
Orchard bees are early pollinators. That's why they are used for orchards. For later garden pollination, leaf cutters are better. You can make similar nest tubes for leaf cutters, but reduce size to about 1/8" - 3/16 ID and about 2 1/2" - 3" deep.
From our limited experience, the biggest advice I can offer is, be patient. It takes a while to establish a population.
Mason bees are the ones you can set up nests for, but they may or may not like your particular location. Miner bees are similar (solitary bees, short active season, but they make burrows). They're on their own for nests. Both are valuable pollinators.
Both have a much shorter foraging range than honeybees, so it is possible to plant for them close to their nests. There are many websites with advice on these bees, but remember that all advice is very local. These bees can be highly specialized to local forage, and you'll probably be happier if you go with the flow for your area. They don't spread far from the nest where they were born, so if you're in an area with none close by, they won't just appear by magic because you put up a nest or plant the right flowers.