Getting a big dress abroad

It depends how bulky it is - if it can't fit into the standard luggage space then you are going to either have to check it into the hold or pay for another seat for it.

I'm getting mime in a travel maxi box from the boutique its dimensions are enough to fit in the overhead lockers but they had a bigger ones too which would go in cargo. I've heard if you're flying business class they might hang it, but wouldnt count on it either way x