If you are strictly looking for a , MAJ Stair is the top recommendation. It is a dedicated freeware extension for drawing various stair types quickly.
To install any of these plugins (Instant Stair or its free alternatives): Creating STAIRS in SketchUp with this SketchUp Extension! instant stair plugin sketchup free download
Vali Architects currently distributes "Instant Stair" as a paid commercial plugin . It is part of their "Instant Architecture" suite. You typically purchase a license from their website or via the SketchUp Extension Warehouse. If you are strictly looking for a ,
is the community favorite for "instant" results without the subscription. and L-shaped stairs.
Most plugins offer options for spiral, straight, U-shaped, and L-shaped stairs.