"What is your car made of?"

Translation: Miből van az autód?

[GregWood15]

Why is it wrong to include "neked"?

[MitjaSterman]

Why is autója also ok?

[vvsey]

Because that would be the formal you, which is conjugated like the third person.
"Miből van az (Ön) autója?"

[Patricia460976]

Can I use "Mit a te autod késült?"

[RyagonIV]

Even with készül (which is the intransitive version of készít. This language is so neat!), it would still need to be miből. Készül doesn't make sense with a direct object.

Also remember the word order: verb directly after the question word.

[Patricia460976]

Ack, right. Word order. I keep making it more fluid than I should.