What would be a reasonable FOSS alternative to Sketchup? I know a number of architects who are dead set on using Sketchup versions circa 2014 - 2017 for most o

What would be a reasonable FOSS alternative to Sketchup? I know a number of architects who are dead set on using Sketchup versions circa 2014 - 2017 for most of the preliminary work. It seems to fit their workflow the best. They only go to AutoCAD when absolutely necessary. We are talking architects with 20 years of AutoCAD experience.