Can i build assemblies with suitescript?

yep.

record.create({ type: 'assemblybuild' })
    .setValue({ fieldId: 'item', value: 1460 })
    .setValue({ fieldId: 'quantity', value: 1 })
    .setValue({ fieldId: 'location', value: 1 })
    .save();

Do i have to enter the component items to save it?