First off, I would advise against using multiple trees for just one wand. That's a tad bit wasteful hun :p
A good start would be finding an oak tree. Connect with it, meditate under it. Ask it for a gift of wood. Some traditions will tell you to wait until a limb falls, and use that, while others will say it's acceptable, preferable or even required to take the wood straight from the tree. Either way, most feel you should ask the tree first, and only take the wood if you feel the tree giving you permission.
Or you could just buy a chunk of oak from the local hardware store. A wand is really just a tool for channeling energy, and more or less anything could be used to make one as long as you are able to move your energy through it.
Once you have the wood, just carve it as you see fit. It doesn't have to be perfect- mine was quite obviously not the work of a skilled craftsman. I actually left mine unfinished on purpose. About halfway through it just "felt done". I was planing a very elaborate, refined design but it just felt "right" the way it was, so I left it.
Decorating is also an option. Crystals come up a lot, and if that strikes your fancy clear quartz is a good jack-of-all-trades type. Of course if you intend this to be a single-purpose wand, use crystals for that purpose. Or don't, crystals or other decorations aren't necessary.
Another thing worth considering, but again not necessary, is soaking your wand in an herbal mixture. I did this for mine, soaked it in a special blend I made for that purpose. I also routinely dust it with powdered ginger.
And finally, consecrating and empowering your wand is important. There are countless ways of doing this- if you follow a specific tradition, they'll likely have some guidelines for this, otherwise just do what feels right. Common elements are cleansing by the four elements and letting it rest under the full moon. Really, it's up to you; whatever you feel makes your wand stronger and more receptive to your personal energies.