Making a spelljammer period falls squarely in the "DM's discretion" category, this doubly so. Generally speaking, that's the answer to any "can I make this" question for something that is not expressly a part of a class feature or spell; making magic items outside of Artificer infusions or cobbling together anything bigger than a breadbox or with pieces smaller than your hand is not something RAW is going to give a player carte blanche to do on their own initiative.
Presuming I had the necessary materials, would it be possible to make a Flying Fortress (think DS9) using a spelljamming helm?
I reserve the right to /stillme for any reason whatsoever.
The fires of Hell scorch you,
My vengeance terrible,
I, ascendant,
Above the flames of
The Inferno,
Of whom the lowest and most torturous
of circles is
Reserved for traitors.
The dead shall
Laugh at
Your eternal fate
Your sins
Shall return
To mock
And torment you.
Making a spelljammer period falls squarely in the "DM's discretion" category, this doubly so. Generally speaking, that's the answer to any "can I make this" question for something that is not expressly a part of a class feature or spell; making magic items outside of Artificer infusions or cobbling together anything bigger than a breadbox or with pieces smaller than your hand is not something RAW is going to give a player carte blanche to do on their own initiative.
The Dragonlance adventure came with FlyingCitadelHelm. It's basically a Spelljammer helm with the purpose of moving a Citadel/Fortress.
In the Spelljammer adventure:
There is a large asteroid powered by several Spelljamming helms.