I would say length by width. "No longer made" would be the correct statement.
Weighing in at around 15 tons or so, but typically only 10 by 30 feet, old cabooses are massive marvels no long made by the rail industry. But if you want a ready-made, weather-resistant and flood-water-lofted house, there are much less adorable places to start your search.(the beginning of article: "Cute Caboose: 7 Train Cars Transformed into Tiny Houses")
10 by 30 feet - is that ratio of length/width, or length/height ?
does "no long made" mean "no longer made" ?
I would say 10 by 30 feet means width by length (10 feet wide by 30 feet long).
Train cars are narrower than they are long, so when it was a train car, it was 10 feet wide. Once it's a house, I guess it's possible for the dimensions to switch. In any case, it does not refer to the height.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
When wrote this: "10 by 30 feet - is that ratio of length/width, or length/height ?" - I wasn't thinking that it looks like I mean that "10 = length" and "30 = width". I was only thinking about length, width and height, regardless of figures.
Regardless of dimensions, I didn't even know what a caboose was. I thought it might be an animal, perhaps related to the moose. I was rather concerned that one might by 10ft x 30ft!
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.