Drawing Curvature and Taper

I suggest working with a local steel fabrication company, who has the capability of rolling your piece. They will be able to tell you what is needed, and help you along your way.

Draw what you want delivered to your loading dock. The development drawing is the vendor's concern. You want to not get locked into a single source.

If the flat pattern is as you describe then when rolled will form a conical tank. Is that what you want?

Look at any good, old drafting book and you will find references for sheet metal development.

Also, you should not use the ID or OD when developing the flat pattern of curved sections. You should use the Neutral Axis. An NA of about 40% is a good starting point for most materials.

Travis