Do you remember when in white dwarf appeared that article by Jervis Johnson who explains how to made a customized vehicle? The same rules appeared in a Chapter Approved book, when Games Workshop didn't destroy every form of creativity yet.
I find this link where you can easily make your own vehicle without too calculations, obviously the above-mentioned article is necessary for a full reference. In 5th edition where the cost of vehicles is heavily reduced, these rules are really disadvantageous.
Hope someone find it useful!
Vehicles design rules
+ Other planes lie beyond the reach Of normal sense and common roads But they are no less real Than what we see or touch or feel. +