The Garden Igloo Kit. in a few different versions. could be a greenhouse +/or alternative to tent accommodations to house a few more summer retreatants. not particularly cost effective though, in my humble view.
21 DIY Greenhouses with Great Tutorials: Ultimate collection of THE BEST tutorials on how to build amazing DIY greenhouses, hoop tunnels and cold frames! Lots of inspirations to get you started! - A Piece of Rainbow (outdoor flower planters)