Take some old bamboos, and chop them into short lengths - if you take out every second node, that's ideal. You then have tubes of varying sizes, open at both ends, with a division in the middle. Strap them into bundles, and put them, horizontally, under the shed eaves, and anywhere else that's sheltered. They'll provide nest sites for a lot of solitary bees.
You can buy mason bee nesters, but bamboo tubes last better, are a lot cheaper, and do a better job as the variation in size allows them to cater for a range of species.
