I will be building a backyard playground this spring.
I have been searching online and most of what I find is "free plans"

I was planning on using pea gravel as a base, but I want to make sure
I have proper drainage.

I was planning on leveling and digging down some with my tractor.
Installing all of the poles
Putting down a heavy layer of plastic
Timbers around the edges to contain the gravel.
Then filling with pea gravel.

But I think I need to add something for drainage.