My first was an aluminum framed one, with flimsy poly panels and top. That didn't last long, even after I replaced the top with glass (hmm, one season's worth there).
So, I ordered this one last fall, which required some assembly (I CAN screw in bolts and fasteners, although it's not my favorite activity). It seems quite sturdy, easy to move around, and I'll see how it works.
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Of course, a rectangle of hay bales with an old window top would have worked fine, too.