Triple Tier Planter | Shop Noise

In this video I make a triple tier planter out of cedar fence pickets. I'm happy with the look of this planter but the plan was horrible! I designed the plan in sketch-up but realized the building process would suck because of how precise I would have to be in order to fit the middle section in the surrounding walls. I did save money with minimal parts but I think a framed triple tier planter build would avoid the required precision.

What do you think, how could I have made this an easier build?