Here's how it's done:
I bought this hinged roof terrarium on Amazon for $20. Then did some layering- a few stones at the bottom for drainage, 2-3 inches of organic potting soil, then 2 inches of moss for decor. I used reindeer moss like this, but I'm sure other mood mosses would work as well.
The green plant growing in there? That's my favorite part. Do you ever buy potatoes, not use them all, and come back from a trip only to find your potatoes have sprouted and started growing? Yeah, it's time to take advantage of that. I buried the potato in there, and with water and a few days of light I had a full leafy stem perfect for mantises to climb on and molt on.
For maintenance, I have a spray bottle which I use every 3 days to spray the leaves, glass, and soil so that the plant grows and the mantises have droplets to drink. The potato plant also grows even faster than the mantises- I've had to trim a few branches as they grow to keep enough space in there.
Some lessons learned- if I had to do it again, I would have used more of a live moss to handle the moisture better without mold. Also, an acrylic or silicon sealant on the main joints and the very top would have made this terrarium a bit sturdier, more water tight, and sealed enough to better keep in the wingless fruit flies I feed the baby mantises.
When it comes to praying mantis husbandry (the actual care and feeding of them), I'll leave that to other resources on the internet. Just know a few essentials from the beginning- A LOT will hatch out of a single egg case, far more than you'll want in a single terrarium so hatch them in a separate container. Also, the mantises will become cannibals after their second or third molt (within a few weeks), so separate them as they grow and focus on a few healthy individuals. If it's a native species, the rest can hang around your back yard. And lastly, a single tub of live wingless fruit flies is enough to feed all of the mantises for the first several weeks of their life, making it relatively easy to care for them at first.