Spaces with low ceilings present a particularly challenging situation for those wishing to use backdrops. And olio drop is a form of a roll drop with a tube is at the bottom. Here are some terrific examples of their use and construction from around the Internet. Credits and copyright belong to those people and sites referred to within.
Above shot of five roll drops in a row from Bryce MacKintosh's Theatre Rigging Refit – Part 1
PDF on building a roll drop, author unkown. rolldrop.pdf