'take downstairs' is grammatically correct and can be used in written English.
It is used when someone is physically carrying or accompanying someone or something to a lower level or floor in a building. Example: "Can you please take the boxes downstairs to the storage room?".
Maybe he'll fix you a plate to take downstairs.
When we were first together, I gave him the garbage to take downstairs.
Whatever the guests were having, we would take downstairs and eat on our laps in front of Coronation Street or Emmerdale.
Put the ones you would like to take downstairs in a bin and leave them by the doorway of your room, with a note attached to it, saying "Take Downstairs", in case you forget about it.
A panel of glass with two bullet holes had been removed from street level and taken downstairs.
I ended up with two bags, which Earle and I took downstairs to the bar at the Ceres Cafe.
The microscopes Once the phones have been dropped, cooked, frozen, rained on, and squished, they're taken downstairs, where the technical stuff happens.
Among the items taken downstairs to the underground car park were a pornographic magazine, pornographic DVDs in a Jiffy bag and a Sony Vaio laptop that held his manuscript.
Eventually, the crops will be taken downstairs and added to the 'aquaponic' system there, where plants are suspended in water nutritionally enriched with the waste products from a neighbouring tank of 80 Tilapia fish.
"After my arrest, I was taken downstairs to a room where, in front of a male doctor, female nurse, and a few female police officers, I was told to strip naked and spread my legs.
In another video taken downstairs (see below), during Kamel's arrest, he doesn't kick his legs or flail his arms and shows no signs of resisting arrest.
