How far do you want to take it? Would you open up the interior of the house more to this area? Would you incorporate some kind of vertical structure at the perimeter?

Take a garden hose and experiment with shapes and sizes. Stick some furniture out there and think about how you plan to use your patio. Use the space, you've defined. That way, you'll recognize that it's too hot and sunny for lunch on summer weekends or it's further from the house than you want to go to set the table. You'll figure out that right size, too.

We would suggest a raised paver patio, like the photos here. You could bring it all the way up to your door sill or have a wide step at the door sill and then step down to the patio (like in the second photo). The use of the patio and your budget will determine how large it should be. Questions to ask yourselves: What will it be used for? Entertaining large groups or small, intimate gatherings? Dining, relaxing? Will you be putting furniture on it? How about a fire pit???

This is a beautiful backyard.