what shoes do i wear?

Sorry if my reply is late but my husband wore black sandals and it looked pretty good.

How do we measure someone for this?

You kind-of don't... There is a tan under-layer that pretty much would fit anyone. Like cutting the head and arm holes out of a large garbage sack and slipping it on. The rest just drapes over that with Velcro to tighten, or loosen. I'm 6'1" with a 37" waist and 250lbs at the time of the event (recreational bodybuilder/lifter). The "Plus size" still needed to be safety-pinned in a couple spots because the Velcro wasn't strong enough to hold, but just because of the weak Velcro on the specific piece. It had enough room to accommodate another 100lbs, but could have been tightened enough to fit someone skinnier. There is a version of this in L, M and S, so I'd just stick with ordering what ever they tend to be and if they are XL or XXXL, get this one. This would work just fine for someone tall and thin, big and muscular, or with a huge belly. And it really does look great for the price. Wasn't sure out of the package, but once it was all on and assembled, it was incredible. Wish I had another reason to wear it... Did I just say that aloud? OOPS!

I am 5'11 with a 38 waist, what size do you recommend?

I believe the Large would be just fine, however, if you will be wearing bulky clothing underneath, and XL would be necessary. My son is 5'11" and about a 36" waist. The XL was a bit large for him, but it was manageable and didn't look like it was too big. If you get an XL, you can always pin it to fit better.