here is an article with various suggestions for how to build floating decks https://farmfoodfamily.com/cheap-floating-deck-ideas/ hope it helps
I would avoid using pallet wood for this. It's not the right dimmensions for a surface that needs to be weight bearing and the types of wood used varies. Pallet wood really needs a solid substrate such as a subfloor or wall before you can install it.
Here is one with a fire pit! https://www.hometalk.com/33068054/pallet-deck-with-fire-pit
If the deck is going to be ground height and installed over a cement pad (or something rated for ground contact), pallet wood might be suitable but I agree with Laura in that it is not a structurally acceptable material for a deck. Good luck with your project!
Here is an idea https://www.popsugar.com/home/How-Build-DIY-Pallet-Deck-41671188/amp
This looks like a pretty easy build for someone using a jig saw.