I use them for anything if I have spare space, but right now I'm using them for gyroids and customised furniture. I plan to use them for pictures later.
I use one as a room of memories from my town, one for pics, one for gyroids, and since I didn't know what to do with my last room, I made some living quarters for Celeste
They're rooms I wanted to display but didn't fit into the theme of any of my houses. One room is the school play from K-On!! where they put on a show of Romeo and Juliet. Another is a ~murder mystery~ room, loosely based on Agatha Christie's novels. Another is a serene Greek meadow room with vases and statues. The last one is a chess room, with the first move already played. It's a shame we can't show off our museums in dream towns.
I'm going to make mine in to seasonal rooms. So there will be a room for winter, spring, summer and autumn. In each room will be items from that seasons events e.g Autumn will have Halloween and harvest festival items with crickets and bell crickets to set the theme. Spring will have lots of Easter eggs and Easter items and summer will be firework themed with lots of cicadas. I'm going to try and make it more event-based so instead of having the creepy set for autumn, I'm going to have all the pumpkin heads, my Halloween outfit and some candy and lollipops, so it reminds me of what I actually did.
I'm looking forward to starting this, each room will be like a vacation to another season
before the update with the storage inside houses, i used to use them as a storage for clothes, hats, masks, and custom dresses. now theyre empty, and i have no clue what to use them for. perhaps extra exhibitions. i know definitely one is going to be an actual star gazing observatory. i miss the fact that the observatory actually was an observatory, and that we were able to stargaze and make constellations. another room could be a labratory to have tests and stuff. but thats all i can think of at the top of my head.
I haven't finished expanding my house so I use the museum rooms sort of as templates for future rooms, like I'll map out to see what furniture looks good where or what wall goes best with my idea for the room.
I had to resort to using mine as extra space. Even after the update that added the huge amount of extra storage I still needed more space lol. I use them like this:
Room 1: Nintendo items
Room 2: More Nintendo items
Room 3: Random items (anything i want to keep but can't use in my house just yet i'll just throw in here)
Room 4: Clothes
Although when i get around to cleaning them out i would like to have them like this:
Room 1: Gulliver Souvenirs
Room 2: Photos of villagers I either had in my town or that i got from wisp.
Room 3: Pascal items
Room 4: Everything you can only get one of and are unable to reorder. For example, the items you get for saving bells in the ABD, Trophies, (even though you can get more) dlc, and pretty much whatever else you can only get once and cannot reorder.