How would I build this?

Want to replicate this for my yard. Around 6 ft x 6 ft so several adults could be seated around it or for kids to play on top of it

I’m a beginner but so far have built a work bench and a picnic table using basic butt joints, lots of glue and screws.

Is this more complicated than it looks? Wondering if I need extra cross bracing underneath to support the weight