2" x 2" pressure treated wood.

Typar landscape fabric.

Pea Gravel

Remove the sod (grass) from the area that you wish to have the patio. Lay the Typar out. Use the 2x2's to form a frame. Drill them for 1/2" rebar stakes. Fill the area with pea gravel. Trim the typar along the outside edges of the frame.

You not only have a temporary "patio" surface. You also have a head start and money invested on building a permanent patio with pavers which should be laid on a bed of gravel for drainage if they are installed correctly.

Pea gravel is usually exactly the wrong type of gravel on which to lay pavers. For that, you'd use angular (rather than rounded) gravel.

Also, pea gravel is not fun as a walking surface, as it moves around when stepped on.