The question about Green house kits availableor not? I don't know if they have that size. I would also say 4 x 4 is really small. My advice always plan twice the size you think because you really will "outgrow" it fast. Buy some electric grey pipe with elbow fittings for arches, 4 18 inch rebar add 6mill plastic. See if this size is comfortable on a 4 x 4 is will be less money for starters.
They have various types of raised bed kits
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