This is one of the most rewarding projects you'll ever take on. It takes a long time but it's entirely worth it at the end!
Step 1: Find Your Lumber
The first thing you'll need is a tree. Well, you don't need a tree, you just need a section of a tree. If you CAN get your hands on a tree it will make the process so much more personal as you watch the piece dry and age.
I saw my neighbours tree getting cut down and asked the guys if I could take a piece of the stump to mill. They were kind enough to cut it into crude slabs which helped immensely!
If you need the stump milled try calling a local sawyer, or invest in a chainsaw mill. You only need the slabs to be cut roughly, you'll take care of the rest with a power tool next.
Step 2: Mill the Lumber Using a Router and Sled
Once the wood has dried to an appropriate moisture level (normally between 8%-15%) you can move onto the next step. This can take anywhere from a year to 3, depending on the species.
In the meantime, build a router sled for flattening wood. I've got a link to that Instructable below:
Apply that method on both sides of the wood until it's flat and level.
Step 3: Continue Refining the Wood
Once you're down to the thickness you need with the slab fill any cracks with epoxy or resin. I only had a few small cracks so I used 5-minute epoxy, but if you had big cracks you're better off using a slow setting epoxy.
Add epoxy to any knots or soft areas to stabilise them.
Once the epoxy has dried use a belt sander to remove the excess and get it down to the level of the wood. After that you can continue up the different grits using a random orbital sander.
I chose to cut the ends of my table so that it was close to square. I like to do this because it makes it more "furniture-like", even though it's live edge.
Step 4: Apply Some Finish and Add Some Legs
This is where the magic all happens. I used a wipe on polyurethane, but practically anything will make the wood grain "pop". Start on the bottom and sides, getting it into the cracks of the bark, then move onto the top. Make sure to wait for the finish to dry properly before moving onto the next step.
I used hairpin legs for my table. I know there is a lot of debate about them these days, but in my opinion they are a simple solution that serves only to highlight the amazing piece of wood on top of them. So yes, they aren't the most spectacular or "pro" way of holding up a table top, but they do have a purpose.
Now make sure to keep a lot of coasters around!