On a finch forum I saw a suggestion to line the inside of the aviary roof with villaboard (cement sheeting) would this be safe for budgies?

I think it would be fine as long as its painted or sealed and budgies can't usually chew ceilings anyway

My suspended aviaries are lined with cement sheeting to reduce the heat effect and I've had no problem with it. Having said that, and as Kaz said, it's on the ceiling so the edges are pretty much out of reach for chewing anyway.

Could you use plywood for lining the roof or would this not be recommended?