Okay, I know I'm showing my dork here, but I just thought of a really really nice kimono-fied uniform for Hogwarts!!
The base of it all would be the kimono - it would be an all-black tsukesage, with a white outline of the Hogwarts crest on the front skirt. On the front of the left sleeve will be the white outline of the Hogwarts castle and grounds, and on the back of the right sleeve, there will be the four House animals (only white outlines).
Now comes what makes the uniforms different for each House! Each House gets different designs on their obi:
Option 1 (formal): Black nagoya obi, with the Hufflepuff crest on the back and a badger on the front. The obiage and obijime will be a choice between pale yellow and canary yellow. The zori will be black, with a yellow hanao and a thin black stripe running down the middle of the hanao.
Option 2 (casual): Pale yellow hanhaba obi with very thin black stripes, and the Hufflepuff crest printed on both sides of each end. Black lacquered geta with yellow hanao.
Option 1 (formal): Black nagoya obi, with the Ravenclaw crest on the back and a bronze eagle on the front. The obiage will be any shade of blue, and the obijime can be any shade of blue or bronze. The zori will have a black base and hanao that is half blue stripe, half bronze stripe.
Option 2 (casual): Bright blue hanhaba obi with very thin bronze stripes, and the Ravenclaw crest printed on both sides of each end. Black lacquered geta with bright blue hanao.
Option 1 (formal): Black nagoya obi, with the Gryffindor crest on the back and a roaring lion on the front. The obiage and obijime will be interchangable between red and gold. The zori will have a black base and red hanao with a gold stripe in the middle.
Option 2 (casual): Bright red hanhaba obi with very thin gold stripes, and the Gryffindor crest printed on both sides of each end. Black lacquered geta with bright red hanao.
Option 1 (formal): Black nagoya obi, with the Slytherin crest on the back and a coiled snake, ready to strike, on the front. The obiage and obijime will be silver, but any shade of green can also be used. The zori will have a black base and silver hanao.
Option 2 (casual): Silver hanhaba obi with very thin dark green stripes, or dark green hanhaba obi with thick silver stripes and the Slyterin crest printed on both sides of each end. Black lacquered geta with silver hanao.
Small accessories like hair ornaments, obi decoration, han-eri, tabi and juban can be modified to the students' liking. The kimono sleeve length depends on student preference, but must be at a minimum of 50cm.
Their kimono will be all black, with very thin dark gray stripes. The full-coloured Hogwarts crest will be dyed or embroidered onto the back, where the center mon is meant to be. Zori will also be black, and tabi will be white (because it's just weird seeing a guy with red tabi :P) Their obi will be hakata-ori kaku obi, in this manner:
Gryffindor: dark red base, gold pattern
Slytherin: silver/gray base, dark green pattern
Ravenclaw: blue base, bronze pattern
Hufflepuff: pale yellow base, black pattern
For the informal/casual version, they can wear heko obi in red (Gryffindor), silver (Slytherin), blue (Ravenclaw) and pale yellow (Hufflepuff) with a pale wood geta and black hanao.
Like for girls, sleeve length, han-eri and juban is up to the students' liking.
For both genders, there will be an awase (lined) version, a hitoe (unlined) version, a ro (summer weave) version and a yukata version in formal (silk) material and everyday (cotton, wool, etc) material. Every student must have at least one of each version in everyday material, and the formal is optional (like dress robes). In place of a cloak, they can wear whatever haori or coat they choose with any pattern on it, as long as it has a base of black or one of their house colours, and the pattern is not indecent.
Umbrellas, raincoats, rain shoes and snowshoes are also their own choice. On bad-weather days, they can wear boots in place of zori and geta.
..... Yeah, I'm really really bored to have thought all of this up :P Maybe if I have a load of free time, I'll draw it out or something ^^;;;
Actually, I'd only thought of the base kimono and the black obi with crests. Then, as I was typing it out, I suddenly began to think of different situations they might have to wear them in, like on their graduation they, they would want to wear something more formal; in the summer, they can't wear winter kimono, etc, so I thought up of the formal and casual materials, the various versions, etc.
Hahaha, my imagination is running wild!! :D And it's so fun!