The best Grounded base locations combine safety, ... One of the first locations in the game you discover, south of the Oak Tree, the Mysterious Machine has a lot going for it.

To build a Grounded grass floor, open the Craft menu and then tab over to the Base Building section (the black icon about halfway along), where you should see Grass Floor at the top of the list.

The world of Grounded looks big, but it will only take a few minutes to walk that distance Your best bet is to head east to the lemon crime punch-o to resupply, then north to the oak tree.