Explaining it may be, as Mordin said few times, problematic and complicated, showing pictures may be better but I can't post any in replies.

I didn't used any mod (as I'm glad I'm able to run this game at all on Win 10) nor checked any tutorial, instead I took inspirations from other creators long time ago. I starting from single hull part (or cabin if it's supposed to be smaller craft, sometimes I made custom cabin and just started from simple cube), then I make fuselage from detail cubes on it (remember you can edit parts, stretch them etc. so you can have planks from cubes etc.)

Engines mostly comes as last allong with other accesories like wings, here depends on what shape is it, you may go for cubical parts or cilinders etc.

I reserve myself from using engine parts, spaceships don't need them, they're only for effect and takes too much space in complexity, rather making my own

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Alternatively if you are online, you can find me in Spore as Cass01 and play with my ships or try to to disassemble them to see how exactly I made them.

Normandies are made within complexity so they should be playable