Are you planning on planting in this gravel area or is it just a gravel surface for walking/ furniture/ recreation activities?

When installing a gravel pathway or patio we try to kill two birds with one type of gravel by using a gravel that has fines (small compactable particles that bind the gravel together ) in the gravel mix.
We excavate down 2 to 4 inches , depending on the profile of the soil , lay double bonded weed barrier cloth ontop of the native soil and install the gravel and compact. The finer textured fines sink to the bottom creating a concrete like texture and the looser larger gravel rises to the top.

If you are using an expensive highly decorative colored gravel that is a different color than your base rock/gravel then a barrier cloth would be wise so the base rock doesn't migrate up thru the colored gravel.

There are several different ways to install a gravel surface for walking and a gravel garden for planting in.

For planting in a gravel garden google Beth Chatto's gravel garden book. There are cross section details that you might find interesting.