Well as to what to get at a pet store, unfortunately most pet store stuff is inappropriate for chins so it's good you are asking. Anyways here is a list,
- food, high quality pellet only food, like oxbow or mazuri, no treat filled foods as it's just junk food.
-a sturdy non plastic food bowl, ceramic crock or metal coop cup work well
-Glass water bottle, they shouldn't get wet so a water bowl is not good and they will chew through plastic bottles
-dust bath, not sand bath (blue cloud is popular)
-either a dust bath house or other container for bathing (glass gallon fish bowls work well)
-depending on what you want for litter, pine or aspen shavings work well. Avoid ceder as it's poisonous
- Hay, any brand will do just make sure it smells fresh, not dusty or moldy and looks good
- Hay holder, not the plastic or metal wire ones though
- Wooden hiding house
- wood and lava rock chew toys
- chin chillers (granite or marble tiles work too)
- wood ledges and perches
- you probably wont find one at a pet store but a gram scale is good to weigh the chins.
Those are what I can think of off hand.
As to the cage I don't have any diy, but you want the cage to be at least 2'x2'x3', taller and bigger is better, you can't go too big, just make sure the chins can't fall more then a foot, so overlap ledges and hammocks. Chinchillas are hoppers, so they don't need ramps, but they love jumping up from ledge to ledge up high. You also don't want any plastic in the cage at all, chins will chew it eventually, and it can cause a gut blockage if they swallow it, requiring surgery to remove.
For most cage items though I strongly suggest vendors on here (banner at top of page and in the classifieds section of the forum), as I said pet stores don't have much good stuff for chins. You can get better, and safe stuff, for cheaper on here then at pet stores. Things like chin safe wheels for example can not be bought in pet stores. Also wood chew sticks at pet stores tend to be over processed so some chins flat out refuse them.
Some other important info, chins are very heat sensitive, then need to be kept below 75F and humidity needs to be below 50% or they will overheat and die. An ac is pretty much required to maintain proper environment for them unless you live in the arctic or high mountains. Also you need to give them filtered water, if your tap water isn't filtered to remove microcysts then you'll either need a filter (brita and pur make good ones) or buy water, reverse osmosis water is recommended. Also very important is fine a vet that treats chinchillas, ideally more then one and one that handles after hours emergencies too. Most vets don't treat or have never even seen a chinchilla, they are exotics so they need an exotic specialist vet, you don't want to get stuck thumbing through a phone book (or searching online) for a vet in the middle of the night as your chin dies. A vet fund/account is also recommended, vet bills for chins can easily get into the hundreds to thousands of dollars quickly.