Its possible to be some sort of factory or aftermarket, but I don't have that much to compare it too.
By any chance do you know the age of the tractor, year it was built or have a serial number for it ? I looked in a military technical manual, in the parts section for a 5R series D6, and if I recall from memory, the 9U series was next and was built well into the 1950's, which I think was the predecessor to the D6B,C and later D series, might be off on that, don't quote me LOL !
In the 5R parts book and as was typical of those tractors, the last several pages usually shows tools, accessories and as is listed in a later printing of a parts catalog for a D7 3T, they show 2 weather cabs, one wood and one metal, for that tractor. The wooden one was the one I was thinking of, and it has similarities to the photo of yours, but is not the same, the side doors look close but the front windows look to be a different size, though I am looking at a drawing, nothing to scale it with, there are no steel upright posts, its entirely wood and glass, and the side doors slide open, having a track mounted above. The roof is sloped the opposite way, front to back. These cabs I believe were typical and likely built for other models like the D6 and more or less probably found in colder climates. I can't recall how long ago, but there is a collector out of Minnesota who used to post on ACMOC/ACME that bought a what I think was a D6 of the early 40's era or earlier, out of Maine that was set up for snow removal, and it was in very nice shape, it was green and it had an original wooden cab that I believe was the same style as is listed in the D7 3T parts catalog I have. This type would likely be of some value as there are just not many of these left intact. I may have saved a photo of it from the sale, but it may be in a folder I have not organized, might take a good while to find it or it could have been lost when I had some sectors go bad in my hard drive, I did seem to loose a couple or one folder of photos of things of this nature.
I think you may have to keep asking about it, but if its something aftermarket, commercially manufactured, it still may have some value to a collector or at minimum to someone who wants to put a weather cab on the same tractor, from the photo it looks solid, but you had better get some blocking under it or that wood which is in contact with the ground will deteriorate very quickly. I don't recognize it as a weather cab produced by caterpillar, but that is not to say I may very well be wrong. The posts with the double gussets look very familiar, there was a style of brush cage/limb risers, weather canopy but not R.O.P.s, that was very common and used that "detail" to attach to the fenders, be them the later heavier type or the earlier thinner kind. Those era tractors did not have R.O.P.S. connection or attachments included in the tractors design like later ones that would allow for R.O.P.S. that would transfer all the weight and then some of a tractor if it were turned over. Now, whether someone built that, fabricated the same style of post with the gussets or its a hybrid of both, hard for me to say, but if it was a good fit, its possible someone may want it, likely not anything of high value, and it seems most collectors of these era caterpillar tractors don't usually have a cab, maybe for looks or what have you, they only use them in the mild weather at shows or around the farm, there sure are quite a few old Cat's working or working part time, really hard to say how long it may take to find a buyer of something like that, if possible I would mothball it, not a huge loss if it were discarded, unless someone else can tell us more about it.