Hoping this is not out of line, but there is a Hand Held Calculator on the website link below that is very user friendly and can layout just about anything, including CONES. You just input the dimensions it prompts you for, including Material Thickness and it will give you all the layout dimension's you need for the layout. You don't need to know the math and its Dead Accurate. It will also give you the degree's and number of "Kicks" for kick forming large heavy cones. You can use the Layout Manual that comes with it like a computer monitor for visual instruction and direction. See the CONE and CONE FORMING pages from the Manual attached below. It will also layout Square to Rounds, Round Elbows, Intersecting TEE's at any angle including the HOLE layout, Stair Cases, handrails and much more. I used the Square to Round & Round Elbow programs to layout the Test Cell Jet Engine Exaust in the photo below. The retainers on the Inlet and Outlet were used for the High Heat Insulation that was applied later. It always reads dimensions in DECIMAL form 1st, then in FRACTIONAL form 2nd, to the closest 1/32",+/- 1/64". This is for the person that doesn't know his/her Decimal readouts. It also has Utility programs for Drill & Tap sizes, Metric Conversions, Pulley sizes, including RPM and Belt lengths and more. This is a hell of a tool for people that don't have any layout experience or know the math. The site shows all the pages in the manual. Be sure to read all the "NOTES" in the pages, it helps things make sense. This Calculator is a Real Tool, its not a gimmick or a toy. Its worth a look at.
http://www.sheetmetallayoutcalculator.com