In updating from some Walmart style particle board and veneer type shelving units to something more durable and interesting, I decided on the industrial design appearance of shelves made using steel pipe and fittings as the supports. The internet is crowded with photos of this style, but I wanted mine a little different and made them lighted with a little steampunk vibe. I also used my water valve light switch, which is an Instructables featured project you'll find here. I recommend doing this using 12V lighting to avoid safety issues, but remember that the wattage capacity of the switch at 12V is reduced. At 12 volts the switch is rated for 5 amps, so that's a maximum of 60 watts. At 120 volts the switch is rated for 3 amps, so that's a maximum of 360 watts. At 120 volts, as this project is, I'm not comfortable going over 150W because of the small gauge wiring used. Unfortunately, I was unable to find any 12 volt vintage bulbs.
After having built this using 1/2" pipe and fittings, I highly recommend doing any sections that require wiring to run through them to be 3/4". It was verify difficult to pull the 16ga wire through the 1/2" pipe and fittings I used and also have room for wire nuts to make connections. If I were doing this project again, I'd use 3/4" throughout.
Decide where you're wanting the shelves to be mounted and investigate what kind of support is available. If you have sheetrock walls, you'll need your pipe supports mounted to studs and possible supported at the floor if you don't have carpet. I had carpet so opted to support them entirely from the wall.
Using a stud finder, locate the studs as best you can and mark them with painter's tape. Also check the top of the wall at the ceiling and try to determine if there is a single horizontal stud or double horizontal stud. Here's a link to an awesome stud finder I highly recommend at Amazon.com. Because it has multiple indicator lights, you don't need to slide it along to try to find the edges of studs. It simply shows lights anywhere a stud is located.
Decide what height you want your shelves at and if you want a support at each stud (usually 16" spacings) or every other stud. Don't try to span a shelf longer than 32".
If you are going to be doing the wiring part of this instructable, I also recommend locating the cross pipe differently than I did. If it were located above the level of the highest shelf, assembly would have been much easier than having it below the top shelf.
You'll be building your supports out of either 1/2" or 3/4" pipe so visit Lowes or Home Depot (L and HD) to see what lengths of pipe they stock, or visit Zoro.com and see what lengths they stock. Zoro will be significantly less expensive than either L and HD. Anything under 14" or so will be referred to as a "nipple" and can usually be found from 1/2" long to 12-14 in one or two inch increments. Knowing what they have in stock, plan out your shelf spacing. Also keep in mind that you lose length when you thread a pipe into a fitting. A 1/2"-8" long nipple is 8" total length, but each end will thread into a fitting about 0.3" hand tight and 1/2" with a wrench. There are resources online to tell you the thread engagement lengths for 3/4" pipe. At the store, measure a tee and an elbow to see how much space they take up, too. Measure, measure, measure.