Try these steps and see how it goes. I've included a SW2016 model and a Step file.
A simple circular extrusion. You can sketch two circles to show the wall thickness, or use the Thin Feature option.
Another simple extrusion up from the center of the first cylinder. I left a tiny gap in this circle since the goal will be to form it as a sheet metal feature (to get a flat pattern). Make sure to use the Sheet Metal Base Flange option to make this extrusion.
The Indent command (Insert - Feature - Indent) will split the 2nd extrusion into two pieces by using the first extrusion as the cutting tool.
Indent will leave an unwanted chunk of material in the center of the first extrusion.
Deleting the unwanted body makes it go away.
Now a cut needs to be made in the top of the first extrusion. I used the ID of the 2nd extrusion, but the OD will work. It just depends on how you plan to fit the parts together. Make sure to only cut trough the first extrusion.
If you unsupress the flat pattern feature, you'll get the pattern for the 2nd extrusion.