An apple crate coffee table is a quick and easy, you can finish in a day or two tops, project that can add a lot of character to any room as well as being a good way to up-cycle unused crates. Don't worry though, you can buy crates at a lot of different stores if you don't have any laying around. It's also a very effective storage space, allowing you to fill almost the entire footprint twice, inside and on top.
This is a project my wife saw somewhere and wanted to do. To be honest she did most of the work while I really just helped out, putting it together for the most part, and documented.

Step 1: Materials & Tools

Materials

4x Apple Boxes - If you can upcycle actual apple crates that's a plus but they are also available from most craft/fabric stores.
Wood Screws - The necessary size depends on the thickness of the wood in the crates and the actual construction of the crates.
Wood Filler
Primer - We went with a distressed sort of look so the primer color was important as it shows through.
Paint - A semi gloss or glossier paint is recommended as it aids in keeping the table clean.
Wood Blocks (Optional) - Depending on the furniture around where the table will be placed you may choose to attach feet to put the table top at a more usable height.

Tools

Sandpaper
Drill
Countersink Bit
Paint Brush (Optional) - Used to apply the paint in a non uniform manner for stylistic reasons. Also necessary if you aren't using spray paint.

Step 2: Prep

The first step is to decide on a layout for your table. There are a few ways you can arrange the crates, a couple of which I've drawn above.The layout you'll see in this guide is is the square with the open center. You could also easily make a bigger table with more than four crates.

Before you start building the table it's best to do some fit checks so the table is as level and square as possible. The crates won't be perfect but by taking some time to try various combinations of position and orientation you can minimize these errors and get a mostly flat and square table. Just keep trying the boxes in different positions until you find how they best fit together.

Step 3: Assemble

With the crates configured and fitted, assembly is a simple matter of choosing your hole locations (3-4), punching them (not critical but it helps in tight areas), drilling pilot holes, and driving in the screws. You should try to drive the screw heads just below the surface. The best way to do this is to use a countersink bit on each hole after you've drilled the pilot. If you Don't have a countersink bit you can use the tip of a large drill bit with similar effect.

When you're done putting in all the screws use a wood filler to cover the screw heads and make the holes flush. As per the fillers instructions allow it to dry and then sand it before painting.

Step 4: Paint

When the filler is dried and prepped it's time to paint. My wife wanted a, for lack of a better word, distressed look, where the top layer of paint is sort of worn away exposing what's underneath (the primer, raw wood, another paint color, etc). From what I gather a typical method for doing this is to paint the top layer as usual and then wear it away through various methods, sandpaper, etc. Instead of that method she applied the primer as usual and then hand painted the top coat with a foam brush. This allowed her to get texture in some spots and control the thickness and coverage.

Step 5: Conclusion

There really isn't a lot to say. It looks good and is more functional than our previous table, as it has more 1st order retrievability storage space. There is a lot of ways you can customize this project, from the layout to decorating it, so don't let the way we chose to do it shoehorn you onto a single path. Look at your space and be creative. As always feel free to ask any questions and post pictures if you tackle this project!