Some people would have to take out another mortgage to buy this.
I'm thinking in residential areas, the likelihood of a prolonged siege against a single garden shed in a single residence among a great many would be a long shot anyway. I'm pondering how I would react to the need for one. I probably wouldn't realize the need of one until the last minute when the danger was right upon me. In that sense, I'd want a safe room within an existing structure so they wouldn't see me traversing from my home, through the yard, and into the garden shed safe room. If I'd had some reasonable advance warning of needing a safe room, maybe I wouldn't want to stick around anyway. I'd think the safe room idea would be security against some kind of mob or multiple assailants type thing.
A lot of ordinary homes have attic crawl spaces. I'd think this would be a good place to hide quickly, given even a bit of time. Most rioters wouldn't take the time to look. You'd have a problem if they torched the place. Unless you had some of those plastic air vents cut through the sheathing. I've crawled through those before I grew a gut. Most modern homes have drywall interiors, you can kick that stuff out to escape from an attic. With rioters still around, there would be some element of danger in any escape.
get a real garden shed and save some money.
The idea of hiding in plain sight is not a completely bad one. With a real garden shed, you could build a false wall in the back which would provide temporary hiding quarters. You'd place the garden tools in front of the false wall. At the speed of most rioters, they probably wouldn't notice the difference in depth. You'd need one of the outside panels to be hinged or whatever for access. And quick escape if necessary.
Somewhere recently, I saw a picture of a pile of logs that was used for covert shelter. The top and side logs were real. Underneath was a hidden room and painted on the doors were the butts of fake logs. From a distance, it was convincing. Not up close.