Not sure why you would need plans for a flat panel door, but I'll give you a few tips.
Make sure there's not a ramp right up againt the bottom of it, it will cause the bottom of the door and the subflooring inside the shed to rot out.
Use three hindges not two, that doors going to be heavy and needs the support.
Use Smart board (sold at Lowes) not T-111. T-111 will rot out in no time.
People like to see those cute cross bucks on the outsides of it. All they do is trap water and rot out the siding and the cross bucks.
We lay the Smart Siding face down after cutting it to size and install 2 X 4's to the back side using Tite Bond II glue and screws from the back side. We make a frame around the outside first, then on acoss the middle then one from the outside corner to out side corner.
We flip it over and install the hindges with through carrage bolts not just screws.