Solitary bees are very useful to us gardeners and are likely to frequent the bee hotels you can make for the garden. They're fantastic pollinators of a wide range of plants, particularly fruit trees and bushes in spring, as being able to fly they can reach these plants in cool, sometimes rainy weather, to pollinate them just when they need it.
They like to make nests in little tunnels, so any old strong bamboo canes with sizeable enough holes, about 50mm wide or more, can be fashioned into a nice little nesting site for them. It's wonderful to see them being used, and you'll be surprised at how many bees use it if positioned in the right spot. Mason and leafcutter bees will use bits of plant leaf to create cigar-like tubes as nests in the holes. Mason bees also like to use teasel and sunflower stems to nest, so these will work too.
For a more secure 'hotel' look, enclose all your stems or canes in a frontless wooden box and hang on the wall.