If the plaster is intact, I would save it and use it "as-is". Drywall compound sticks nicely to both plaster and drywall, and you can blend between the two pretty easily.
If it's cracking and falling apart, then drywalling over may be the easiest and best way. I used plaster washers to keep the remaining plaster in place (visible in 2nd pic near drywall edge), and then screwed drywall right over it. I've seen people put furring strips up first, but the ceiling plaster and lath is so thick that I was worried that even 3" screws wouldn't reach through all the layers.
Here are a few pics of the ceiling progress. You can see where I extended the one wall up with framing instead of demolishing the rest of it.
This bathroom was carved out of the room next to it in the 1940s, so there's some old hackwork in there.
We're almost ready to tape and mud and then start painting.

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That's pretty much what we did...

That would be great!!! But I don't think I can afford one now...and I have reached my 20-game saturation level anyway.
I played a lot of Safecracker when it was at Lyons Classic Pinball. I've got a pile of the tokens around somewhere...
It was on loan from Dean Grover, who worked on the software for that game at B/W in the 90s, and played in the local Mile High Pinball League. You can see his name in the right outlane ("F/X: Dean Grover"). We always thought it was cool to play with someone who's name is printed on the playfield!
If you turn Safecracker on when the date is October 24th, it will display "Happy Birthday Ryan and Amanda", who are Dean's kids! How many kids get their birthdays memorialized on a 90s Bally DMD?
I've played Safecracker with Dean and with Ryan...Amanda wasn't so big on pinball.
I also played Safecracker and many other games against Escher Lefkoff in Lyons. I even beat him a few times...because he was 6 years old, LOL!!!! He beat the adults plenty of times, enough that we never "held back" against him during tournaments. That's why he's so good today.
Good memories from Lyons days...

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We only heat/cool the parts we are using, which is a small percentage of it all. The hallways get very chilly in the winter!
The upper 2 floors that we use as our home are about 4000 sq. ft. total, including the halls. There are separate electric meters for each of the 5 former apartments plus one for the Bank, so we know exactly how much we are using everywhere.
The previous owner took out the central steam heating and installed electric heat. He also removed a hanging gas heater from the bank lobby, but it would be pretty easy to hook up again.
We want to start installing solar panels soon, since we have a lot of unobstructed roof space. Then, electric heat makes more sense.
We get a lot of passive solar heating on sunny days - the stone and brick absorb the sun and it warms up the whole building.

Some progress is starting to be visible...
Amazing how much material is needed to fix up an 11'x5-1/2' room. We did add about 64 sq.ft. of wall area by removing the drop ceiling.

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The roundhouses were built in 1852 and 1855, and were repaired after being attacked multiple times by Confederate raiders. They were torn down between 1905 and 1918 when the B&O was modernizing their shops.
Our cupola seems to have vanished sometime in the late 1940s to early 1950s, probably because it was needing repairs and looked "old-fashioned" by then.
Many historic buildings were butchered in the name of modernization before we learned more about preservation.
We've thought about building an observatory dome in the general shape of the old cupola in memory of my Dad, who loved astronomy.

Last month's Halloween decorations. Cindi usually does more, but we're really busy working on the inside of the house...
Google Street View came by here several years ago, around 2015, shortly after half a block burned down across the street from us. You can see our Halloween decorations from that year, and the generally run-down condition of our town.
Here's a link that should take you straight to the street view in front of our house:
https://maps.app.goo.gl/hg3MhQvjSamwAjiz8

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Nope, that's just an area where it was not really repairable. The bathroom wall below the window and a wall downstairs are getting plaster next. I'm worried that it's too cold to plaster now...might wait until spring.

We've got PLENTY of raw brick at our warehouse! We originally bought a 1904 warehouse and were planning to live in the old offices. Once we were able to acquire the Bank, the warehouse became our storage unit and garage. Eventually it will have living space fixed up in it.
The office needs some plaster work - the whole warehouse is another giant black hole of a project...I'll post a few pics of the office when I dig through my photos. The interior pic below shows part of the 4th floor...there's a freight elevator, too...

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A lot of people in the States go Halloween-crazy! Those bank windows are about 5 by 6 feet, and just beg to have displays put in them. We want to try projectors next. There is nothing going on in town at all, so any displays are morale-boosters.

Thanks, you guys! The warehouse is what drew us out here. It is a type of building known in the U.S. as "Mill Construction", with thick brick walls and a massive interior wooden structure.
It needs a LOT of work, including a bunch of plaster in the office (pics soon, I promise), but most of the space is useable and dry. The freight elevator works, but will not go all the way down to the first level due to warpage of the wooden elevator tracks.
If any of you old-building fans somehow find yourselves near our area, I'd be happy to give you a memorable tour! It takes a couple of hours just to see every level of every building...
There weren't too many artifacts from the old Grocery Company days, but there were a few things. Pics will be posted as I dig them up or retake them...
Compare this picture on a 1906 invoice to the picture I posted yesterday...you can see how they had their own railroad siding and loaded directly in and out of boxcars. The siding no longer exists, but you can still see the bricked-up loading dock doors today.

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Took a few pics in the old Piedmont Grocery Company offices today...all of the material around the windows is plaster on brick.
We want to open up all of the bricked-up windows and make an apartment out of it.
When we first got the building, the office was filled up 4 feet deep with trash and tires and junk.
Why did they use that hideous green color in many 1950s offices?

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Yes, stop by next time you are Stateside!

Here's an interesting article about how to make plaster walls flat and true. You use plumb dots and screeds, of course!
https://www.adrianwest.org/plastering/dots.html