"Close to the Station"
As you exit the Tokyo Big Sight Station ticket gates and head left, away from Big Sight, you'll find the Oneza Ariake Bay Mall, a commercial and office complex.
Here's an introduction to the 2F deck of the East Building of Oneza Ariake Bay Mall.
There are many tables for four people lined up under a slanted glass roof.
Tokyo Big Sight Station is right in front of you!
You can even do remote work in front of Big Sight Station.
I think it's convenient for eating lunch boxes or as a meeting place near Tokyo Big Sight.
Also, there are several tables in front of the entrance to the Bay Mall's restaurant area.
It's under the eaves, so it seems you can avoid rain and direct sunlight (a little, because of the glass).
In addition, there are many tables inside when it's crowded.
So, why not try using these places as rest areas near Tokyo Big Sight Station?