Q.Rooftop Planter Box
I have a pergola that is situated on my rooftop deck. It has the 4 x 4 beams. I was looking to see if there were any plastic square planter boxes on the market that come in pieces that I can easily assemble around these already attached beams without building them from scratch? As in the beam would sit in the center of the planter. My end game is to grow some ivy to climb up the pergola without using stand alone pots that are placed alongside the beams. Can’t seem to find anyone that makes them so I know this is a long shot question!

Certified GKH Gardening Expert
I can't recommend specific places or brands to purchase things, but you might try hydroponic grow trays and flood tables You'll have to specify deep tables. Modify them with drainage holes. They make them in just about any size, but 4x4 is very common.
This collection of article will offer more information about container gardening once you DO get a suitable container for the area.
