Originally the layout was going to be much smaller and was going to be retrofit into a fairly large bedroom in the house. However, I finally got settled in my life and was able to build a shop in 2020 during Covid for working on and restoring/storing vehicles and doing other projects, so when I decided on that building, I designed it with a gambrel roof and created a loft above the main level. The loft in the rafters is 18'x64'. I wanted some of this for storage of car parts and other household items. I decided I could give up a good amount of it though for a fairly large layout, so I planned for an 18x40 area, however the rafters went to 39.5 or 41.5. I chose to use the rafter at 39.5 for an 18x39.5 foot room or about 711 square feet. 

Here is a picture of the loft area before starting on the project. 

September 2021: Here is a picture of the wall after installation. If you look really close you can see all the outlets in the room as well. After the wall was built I also installed some outlets in the ceiling as I had originally planned to use hanging LED shop lights, which you can see on the floor in that room. 

August 2022: The next project was to put up the insulation and then install the drywall. Here is the start of that project as you can see all the insulation up on the walls and ceiling and then the installation of the first piece of drywall on the ceiling. 

February, 2023: Here are pics of the room with the drywall finished looking in through the wall without drywall first and you can see the lights installed on the ceiling with the outlets controlled by 2 different circuits on separate switches. The second picture is from the back wall of the layout room looking towards the finished wall and doorway. You can see the outline of the layout on the floor in black spray paint. 

March 2023: Now it was time to tape and mud the seams of the drywall. While I have done this before on smaller projects I thought I would just take this on. As an aside, the main shop floor is 40x64 w/13' ceilings and I did everything except the ceiling drywall (I didn't have a drywall lift that could go that high). Since I was having someone do the ceiling drywall, I had them do all the tape/mud and sanding on the lower level walls at the same time. I should have had them do the tape/mud in this room too! I'd be a year ahead of schedule!

February 2024: Note that it took almost a year from the time that I started the mudding to finish because I forgot how much I hated that job. Unless you do this job all the time, for your job, I recommend farming it out and saving yourself a LOT of grief. At any rate I did finally finish it and started priming and painting, but not before I decided to change the lighting to some dimmable LEDs in the ceiling, so I had to crawl up in the rafters and run new wire and install a bunch of electrical boxes for the new lights seen below. That wasn't a fun time, but I planned appropriately to be able to just crawl up there once and feed all the new wiring in the electrical boxes in that one trip.

Something to think about when building a train room. Don't forget a space to have a workbench to be able to work on trains or models etc. I didn't think about that until my wife mentioned it. So at that point it was time to move part of the wall and create an alcove. Thankfully this took me less than a week to deal with. You can also see the initial blue paint on the walls. This added about 28 sq feet so the room is now about 740 sq ft. 

March 2024: I installed some additional outlets in the alcove area and a desk and a chair I had that were not being used. The floor is Mohawk laminate flooring. I installed the door casing and all the baseboard molding. I am really happy with how it all turned out. The room is completely finished and ready to build the layout now. 

It was done after the layout construction but here are a couple photos of the mini-split used for air conditioning and heat in the room. It cools really well but haven't really used it for heat yet in the winter as haven't had a chance to spend much time up there in the winter yet. will need to keep it running constantly once start running trains to keep the room conditioned but until that time it is only being used intermittently. 

After deciding I needed a better switching yard instead of putting it under the layout, I decided to make a little more room in the loft to build another extension to the train room. I decided that this room would be separate from the main room and that trains would go through the wall from the main room into the switching room. From the layout room I will have trains just disappear amongst trees into the wall. From the yard side, the train will go through a "mountain" against the wall. The "mountain" is necessary to cover up the coolant lines for the mini-split system on the wall. Here's the start of the construction of the walls for the switch yard room.