There are many plans you can get online and have a local handy man put together you. You can buy pre-made at the lowes or HD.
One idea is wrap the 3 walls up high with this style very cost effective.
About $20 per foot running foot in materiel.
A handyman can build each 10' section in about 4-5 hours, so at $25 an hour labor you can figure $125 per 10' length. total $325
Here's the plans