Redwood will rot with dirt touching and regardless of rot will allow the plant to run unless it's 2 to 2 1/2 feet down plus has a poly rhizome barrier. I'd jst purchase a rhizome barrier. Check your local roofing supply company for commercial grade poly to use as a barrier. Rgds

Is this to be a "raised bed" or an actual "container" with a closed bottom?

I assumed the latter, and would recommend cedar wood for the building material.

Josh

sorry for not being clear, the project is a standalone container sitting on concrete slab. Potting soil will be used instead of heavy soil.

Does cedar last longer than redwood?

We have put a pot of bamboo in a 15 gallon nursery tub and it grew very well.

What about plywood construction or use plywood as a bottom?

You don't need a bottom at all. If it's sitting on a concrete slab, all's you need are sides, like a raised bed.

As for constructin materials, you could used treated wood, or that polymer/wood composite stuff used as decking. Or, you could use those interlocking retaining wall blocks; that's what I use (though a little spendy $$$).

Cheers!

On second look, forget the retaining wall blocks; your space is too narrow to accomodate them.

And another thing; your proposal will act like a container rather than a raised bed on top of native soil. As such, there will be no natural wicking action from underlying soil. You will have to pay close attention to your soil constituents to ensure longterm health of the planting. Peat-based commercial soils in containers (which yours will be) will badly compact over time, and drainage will suffer. Accordingly, if it were me, I'd be making my own soil mix. And even then, over time, you will probably find that you will need to remove some soil periodically, and replace with new stuff; kind of like re-potting a container planting.

Good luck!