The German restaurant where I worked was famous for their 'giant' cream puffs. The shells are at least 6" in diameter and 4" high. I know they used commercial convection ovens to bake them, but that is all I know. Is it the fan that gives them the size? I tried to bake them in a conventional oven and failed. Small ones, no real size. I have seen them in grocery store bakeries in that area so somebody knows how to make these. Can anyone tell me how to make these huge choux pastry shells?
You haven't really explained what you did, so it's a bit hard to give useful advice on how to overcome a failure, but my patê à choux pastries have always come out sized proportional to the amount of pastry I use.
Since choux doesn't tend to spread much, make sure your base is close to the diameter you're after; I just pipe inside out, creating a connected spiral, until I reach the desired diameter. I continue piping inward through the middle of the original grooves. My preference is to make tiny ones, but if I needed to make larger ones I'd just continue spiraling in and out as needed until I get to the point where I only have a "tip" left. With a typical Ateco extra-large tip you'll probably get about an inch of puff for each layer, so you probably just need about 3 layers, because you can probably compensate with an overstuffed filling. With more layers than that you may lose structural support.
Some "giant" cream puffs I've seen online just used a large ice cream scoop, but I think that'll probably only get you to about 3-4" diameter at the most. If you don't like the piping approach, you might cluster three scoops near each other and wet-pat them so that they touch.
From then on, it's just a matter of adjusting time and temperature. Larger ones likely need a longer baking time. Additionally, larger ones may benefit from a larger proportion of egg white to encourage a bit crisper outer layer.
I have recently come across a way to keep the shape of hollow pastries during baking:
Wrap your dough around a handful of marshmallows. The marshmallows will hold the dough structure while the dough expands and hardens.
The marshmallows will eventually melt in to a pool of sugar at the bottom of the pastry that you can remove or leave in as a surprise.