Even though there isn't a method from with Design Database to delete roof drawings, it is possible to do so by manipulating the files in your project.
Ensure you have backed up your project before attempting these methods.
From within Design Database, identify the roof name that you wish to delete. In this case we are considering "Roof 2"
Completely exit Design Database and ensure you have a viable backup of your project. We will not be able to repair your project if it is damaged.
Using File Explorer, navigate into your project folder, and identify the DDBROOF.NDX file.
Open this file in Notepad, and examine the data for the roof you wish to delete (1). Take note of the number to the left of the roof name (2)
Fully delete the line that contains your roof name. Do not make any other changes to the file other than removing the line.
Save the file back into your project. If you are asked if you wish to over write the existing file, select yes.
Examine your project folder to locate the ROOFPOLY.* and RLIGHTPOLY.* files. Identify the files that have the same extension as the number noted in the point above. In this instance, the number was 2, so the extension we are looking for is .002. If the number had been 20, you would be looking for an extension of .020
Delete the corresponding ROOFPOLY and RLIGHTPOLY files. You should now be able to load your project back into Design Database, with the offending roof removed. Removing the roof will have repercussions on your project. Be sure to run the Set up Intermediate Floors/Ceilings, Set up Ground Floors and Set up Roofs methods before running any calculations. If this is a PartL project you will need to re-run those calculations.