As an example, if you look how phpMyAdmin handles adding new tables, that's the
general idea I had in mind. Essentially, allow the user to enter either the
number of fields or the list of fields (perhaps include a prompt for the
separator, or assume whitespace).

Then, list all those fields in tabular format, allowing the user to change the
field type and other common attributes. Personally, I wouldn't worry about
allowing the user to enter specific info at this stage for the more complex
field types, such as radio buttons or lists. It's easy enough to click on each
field afterwords and enter the custom data then, such as the possible options.