I would prefer to keep/fix the existing body panels. If you were to replace the roof, look at about $800-1000 just to R&R, no paint.

The decklid and the rear panel...Figure a good used desert decklid and panel $500, paint blend $4-600. Repair roof and blend paint $1500-2000. That roof dent does not look that bad...at all. But bodyshops see a 67 Firebird and the cost will more than likely increase. I say that dent is a $1000-1500 repair.

If say you were going to eventually repaint car to a different color is something you should think about.

I say take a breath, a step back, re-evaluate and assess. You know you need the trunk and deck panel. If the car is a nice original and or worth it, the price difference between used excellent original panels and repops is probably $200-300 more for both. And you know that originals will fit (thus saving time and labor costs at $65 an hour to fit will be negated)