Size: First thing to consider, Artificial grass is expensive. I found that the minimum size of a par 3 green is 60 x 60 =3600 sq ft. For a chip and putt it was 30 x 30 = 900 sq ft. The price for artificial grass for the green was $.60 sq ft. up to $4. I went with the lowest price. I could always upgrade in the future. To make a chip and putt size (900 sq ft x .60) would be $540 just for the grass, not including any rough around the green, or material for underneath.
I understand why estimates to build a putting green of 2000 sq ft are $15-25 sq. ft.
I decided to make my green just under 720 sq ft. or 24 x30.
Build: Remove sod. Backfill with dirt to bring it above the ground level and angle so water will drain off. Where did I get the dirt? I dug out a big bunker.