Making Ship plans

A general question: Given ship stats, and a picture, as in the Rebellion
Sourcebook, where is a good place to start if I want to draw ship plans?

The specific project is the TJ-type Transport.  How big is the silly thing?
I know how much it displaces in liquid hydrogen, but that means little to
me in terms of size...  Am I missing something, or are there a number of
"correct" dimensions?

                                   -Bob

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