If you do not have a patio and you want one added to your yard you should talk to a professional landscape architect or garden designer. They will make sure that you get a patio that meets you needs and they will be able to help you decide what to consider in order to use the patio all year round, how big it should be, what type of patio material to pave it with and what type of roof covering you should use.
Deciding what you want to use your patio for is the first thing you should do before contacting the professional architect. If you want the patio for entertaining it will need to be large enough for patio furniture and a barbeque as well as for people to mingle. If you want to use it to relax, then you want enough room for a daybed of other furniture that is protected against the weather.
Planning out patio should also include the type of plants you want to add to your garden. You can use potted plants, plant shade trees and plants, and even add a sculpted garden bed. If you enjoy cooking, consider planting an herb garden where you will always have access to fresh produce.