The Carlson Compact and Secure Double Door Metal Dog Crate in size intermediate is one of the nicest dog crates I've used. I have two miniature pinschers that I crate together at night, so this is the perfect size to house both of them with plenty of space for toys, or for a much larger dog to restrict night-time movement. The intermediate size is 36" long, 22.5" wide, and 25" tall.
The crate ships in a cardboard box and it easy to assemble. It's just a matter of lifting the top section and allowing the sides to come up with it. Then you use the clamps to secure the ends.
The crate comes with an insert panel that you can use to divide the interior space if needed. This would be good if you want to keep dogs separate, or minimize the space a puppy has as it grows. In this sense it's modular and will grow with your dog.
The other fantastic feature of this crate is that it has two doors. You might wonder why this is necessary, and I can give you two good reasons. First, if you are using the separation panel it will allow two small dogs on either side to exit/enter at the same time. You won't have to mess around with opening/locking two doors. Second, if you like to move your crate around, you'll find that it doesn't always fit perfectly in one position. If you want to use it the wide way, you can use the larger, wider front door. If you want to use it the narrow way, you can use the narrower end door. Each door has two slide locks that are very durable. Some crates come with three, but it can be cumbersome latching them all. These are positioned so that just two locks will secure the door for most purposes.
The metal wire is coated so it's not rough. There is no material flaking off. In the bottom is a single rigid slide-out tray. It's about an inch deep so will contain "spills". The tray slides from the front (wider side), easily. Cleaning is a breeze. Simply slide out the tray and spray it down. Because the intermediate size crate is a standard size, you can find a lot of cushions to fit it perfectly.
The wire slats are about 1.5" apart, narrow enough to keep most dogs from getting their noses out through, though a chihuahua or other tiny dog might manage it, but they definitely couldn't get their head out.
The doors swing rather stiffly, but this should loosen up at they are used. The crate itself is quite heavy and it didn't come with handles to allow for easy carrying. The crate also folds down easily for storage or transportation. Once it's folded there is a latch that holds the panels securely in place.
All in-all, this is a fantastic crate with multiple uses, whether it's for a single large dog, multiple small dogs, or to grow with your puppy.