Question
I have an area about 15X20 that I dug out and put gravel in, about 4 inches deep. I was going to put in concrete, but have since changed my mind. Can I place decorative rock
over this and if so what would be the best type, also would a have to place a fabric barrier.  Thank you

Answer
The short answer is yes you can. As to what kind, you can use what ever you like but if you plan to walk on it and use it under tables, chairs, etc...then the best rock is fractured gravel of smaller size. Crushed slate about dime sized is really the best. But crushed brick is also good. Larger rocks wont be comfortable. White rocks will be bright, and pea gravel will move around too much.
You don't need a barrier but if you want it might reduce how much decorative rock you need by limiting the amount of fine materials that settle into the gravel below.

Best Luck

Sean Murphy
Amenity Architects, LLC
www.amenityarchitects.com