First fashioned from a modified birdbox in 2001, adding canes of old Japanese knotweed and bamboo, not finished until some 14 years later this May, then put up on a wall at the rear of the garden (SW facing). After which Red mason bee Osmia bicornis started moving in after about a day.
Following advice and the findings of the BUGS project in Sheffield (www.bugs.group.shef.ac.uk/BUGS1/sources/bugs-reprint2.pdf), a mixture of cane sizes with different diameters were used. A key factor seems to be to place in full sunshine, so fixed on a south facing wall or fence. Through the months, various other species have taken up residence. The plugs of mud, capping the end of the brood chambers, are the work of Osmia bicornis, and the plugs of chewed-up vegetation are from Osmia leaiana or Blue mason bee Osmia caerulescens.
A shop-bought one has been lying around the garden so I put that up too; this took slightly longer to be found and colonised, but both have been successful.
For a lovely 15 min video about some garden solitary bees, check out https://vimeo.com/129712987