What Dwemer ruins have storerooms and where are they located? The only one I know of is the one at Mzulft, which is outside and just down the path from the entrance.

Define Storeroom?

All larger Dwemer Ruins have smaller interior rooms that are behind a solid door that needs to be unlocked, or have a trap that may need to be disarmed to reach, and do not need to be opened to complete a trip through the Ruin. Blackreach has the largest access to individual cells, but Mzulft has just as many sections behind a solid door as Blackreach. Avanchnzel is the third, Nchardak in Solsthiem has many hidden areas too.

Mzulft is the only dwemer ruin that has its own unique (and separate) storeroom, but there are areas in other ruins that contain a lot of dwemer metals and other dwemer objects (if that's what you're looking for). Nchuand-Zel, Mzinchaleft and Avanchzel are several that seem to have a lot of dwemer stuff lying around.

It's just that I use a mod that says there's extra stuff relating to it, usable items, that have been placed in "Dwemer Storerooms". Whether other storerooms are called such I wasn't sure about. Obviously they're not...

Alftand has a small ruin next to it that allows access from the ground to the glacier. Also Reachwind Eyerie in the reach is a small tower with plenty of Dwemer clutter in it.