First I would like to say how truly easy this project is, (No joke, I'm 14 and I did it all but driving to get parts) I managed to finish it up nicely after about a week of 1 hour per evening working on this thing.

I built it to hold my expanding array of servers, stacking them up in the spare bedroom wasn't working. I needed a solution that would remain neat, tidy, and it needed an aspect of professionalism. The total cost was around $25 for everything, so this was perfect for my needs, and hopefully will be for yours.

Step 1: Materials and Tools

These are the things you will need:

Tools:

-Drill

-Mitre Saw (A hand saw will work, its slow though)

-Hammer

-Tape measure

-Pencil/Sharpie

-and a rackmount server will be handy for test fitting

Materials:

-Lumber - I used 5 8 foot lengths of 2x4

-Metal (The rails used to support the servers)

-Various screws/nails (I used both)

-Casters (Optional, but handy)

I think I have listed everything, Spam the comments if I missed something. :)

Step 2: Measurements

This design should work for most sizes of rack, but If you are going to do a full 42U cabinet, it might be a good idea to add more support, remember how heavy servers are! (A fully loaded 4U server can be 150 pounds, so add 10 of them and you have some potential issues)

These are the internal measurements, you will have to do some math to figure out the outside, or lengths of the wood.
Height: 28" (16U [16x1.75])
Depth: 32"
Width: 17.75"

I began by cutting the pieces that make up the inside of the width, this gave me a gaurantee that the servers would at least go in, maybe not the right height, but they would go in.

The formula for figuring out how tall to make the inside of the rack is here (For all you math people)

H=1.75xU
H is height, and U is how many U you want your rack to be. Remember also that if you make it taller, you will need more lumber.

Step 3: Conclusion

Use the same principals for mounting more servers, and other than that, you are done! Put it where you want and wire everything up!

When I get more servers, I will add pictures of them mounted.

Good luck!

Step 4: Begin Framing!

This should be fairly straightforward, Start by making the two ends of the rack, and then build the pieces that hold them together.
I included a couple pictures of how I started, and finished. If you find a better/stronger way to frame your rack, use it. My way was meant to keep the rack further off the ground because my basement where the rack is going to stay, happens to be slightly prone to flooding.

Step 5: Casters!

Casters are optional, but recommended, the rack will be very difficult to move without them.

Just as long as you don't try to drill into existing nails or anything, this is the easiest part.

Step 6: Labelling the Frame

It proved very useful to label the side of the rack, This is very simple. Take a tape measure and make a horizontal line every 1.75", then write the number and a big U if you want.

Step 7: Rails

The rails on this rack rely on the little lip that the top of most servers have, otherwise you will have to improvise, and I'm not sure how this would work for 1U servers, because not all of them have the little lip.

Try to find where the server is going to sit, then find the distance between the indent under the lip, and the top of the server. Take that distance and put your rail that distance away from the top of the "U" you want your server to inhabit. Mark it with a sharpie and then drill the holes where the screws are going on the rails. After this you can screw them on.

Step 8: Mount Your Server!

For the actual mounting of my server, I left 1U from the top of the rack, this served as a nice place to stash keyboards, hard drives, graphics cards etc.

It might be a good idea to remove any easily accessible hot swappable stuff from the server for this step, It makes the server lighter and will provide more places to hold. Other than that, Having another person to help you align it will help, but other than that its just a matter of not getting the whole thing crooked.