I just finished putting Hulkbuster together he has to be the most amazing statue I own so far I think Hulk transformation will be just as good!!
I recall someone asking how big is he and how much room you may need. Below are some dimensions that might come in handy.
For the depth you're going to need 500 mm but I suggest 600 would be a better comfortable fit, 20 to 24 inches.
for the height, in this configuration it tops at 730 mm 28.7 inches, but if you're going to put Iron Man inside him I suggest at least 1000mm, 40in This is just a suggestion as I have not as yet tried to put him in yet.
and the width you can get away with 1000mm, 40in if you put them close together but ideally 1200 would be preferable, 47.2 inches.
I'll be taking some more images over the weekend.