The rooster shed is working well at reducing noise; actually I should call it a 'breeder' shed.
It was an old cubbyhouse that I've lined with extra boards, some old real estate signs (glued to the ceiling) and some carpet. The back of the door was doctored by gluing neoprene over it. The neoprene (wetsuit material) overlaps the jamb so it helps stop sound bleeding around the door edges when the door is closed. (As you can see in the photo the door is slightly ajar.)
A hatchway at each side faces onto two different pens. Originally I did it that way (putting a sound-deadening hatch at each window) so I could alternate use of the pens to keep the ground from developing a huge parasite problem. However as I raise more birds I'm finding that I want to keep several roosters, not just one.
This brings up the obvious issue: noise. I can't very well have a sound-deadening shed for one rooster if another 2 or 3 are crowing loudly outside. Yet roosters often don't get along when they're with girls.
So the answer I found was to divide the sound-insulated shed in two and use both pens (one housing juvenile cockerels, the other the rooster and hens). Here are the separate hatchways opening onto each pen. You'll notice that each side has a roost just inside the window ledge.
The division inside the shed was made of some c-clipped mesh panels that keep themselves upright (they aren't fixed to either wall) by being a bit kinked (like a concertina) and having one end folded to form a perpendicular brace. (In plan view it looks a bit like an L.)
The end of the 'L' is tucked behind some nestboxes to help keep it steady.
On the other side the division only just reaches the wall and isn't permanently fixed there either. I hook it to the wall both top and bottom so there's no chance birds can squeeze through. Meanwhile I use this section as the doorway. As all the panels are c-clipped I can fold the divider out of the way whenever I want.
At night, all the birds roost in the same shed, and if the crowing is too loud with the hatches open, I simply close them. The structure is big enough to supply air all night, but there are also vents (which were part of the original wall) and they don't seem to let too much sound through. As the shed is fairly dim it's unlikely I'll see bad squabbles between a rooster and cockerels when both lots are inside. I can always place some shadecloth down low on the divider panels if that happens.
It may look fiddly, but this represents about $50 of investment and took an hour to set up. The galvanised panels came in sets of 4 'compost panels' for $26 from Bunnings. Yet making the divider has solved two problems at once: how to keep more than one cockerel and how to keep the noise down (by using one shed as two).
Just as a side note, keeping a lot of young cockerels in a pen of their own is only possible if the birds are either naturally placid or have been raised together, and a few of the highly aggressive breeds will never suit having an all-male pen. But given that I only keep placid birds, this lets me at least double... heck, triple or quadruple!... the number of adult males I can keep before I start seeing (or hearing) problems.