So this year for Halloween I put together a helmet designed after Lando's skiff guard disguise in Return of the Jedi. Among the valuable & helpful tutorials I found online were this Instructables guide on making a cardboard helmet, along with this Pinterest pin covering similar ground.
There are no existing plans for the Lando helmet, though there are plenty of plans for a Boba Fett one! I ended up using a couple of reference pics from Google, including the ones from this Dented Helmet discussion thread. The helmet ended up being smooth across the top, instead of the wavy form that you can see in the photos. If I were to do this again, obviously I would have tried to match the contours more.
The helmet was a quick build, even for a first-time builder. I followed the tutorials' advice and started with a network of curved pieces, held together by a base. I was able to cut out small cardboard pieces and attach them to the ribs of the helmet to get the curved top pretty quickly. The visor and cowl pieces were just simple guesstimates based on the dimensions of the helmet, and the front piece covering the face was held in place by paper fasteners from Staples. (And the white teeth were colored using Wite-Out from Staples as well!)
The inside had a bunch of foam hot-glued inside for comfort. Passing the sides was a little more difficult, as I had to worry about the hinges of the front piece. In fact, my first attempt at passing inadvertently put glue all over the fasteners, preventing the piece from hinging down! I had to quickly pull out the foam (learning in the process how well hot glue holds together) and attach the foam to the rear of the helmet, covering the hinges to provide enough padding so that the helmet would not move side-to-side.
I also put together a small chest piece that was in the same basic shape as the one Lando wore. This was done mainly so that it wouldn't look weird if I was just wearing the helmet and nothing else. This piece was again just a simple guesstimate of its dimensions, taken from Jedi screencaps and other reference photos. It was held in place by black gaffer tape.
About 4 or 5 people at the party I attended were able to identify the helmet from first seeing it, and about a dozen others recognized the reference when I did the Lando helmet pull-down (the Star Wars equivalent of shade tippin'). The rear cowl, held in place by gaffer tape, was starting to come loose by the end of the party, due to body heat and sweat. But it was durable enough that I made it through the evening with a load of compliments about the costume.
If I had cared more about the helmet, and if I were going to use it again, I probably would have invested some more time in coating the outside with resin or something to make it a more durable and smooth surface, but for a one-time costume it was plenty durable enough. It turns out that hot glue is rather good in keeping things stuck together! I'm looking forward to next year's costume, when I will most likely get to use the glue gun again.