I just bought a Tacoma this week and haven't really decided what setup I'm going with for my bikes. I'm definitely not going with rocky mounts because several of my bikes are thru-axles and it's a pain the take the front wheel off.
I don't have any dimensions for you, but if you build one make sure you take into account the width of your widest bike tire. I have several styles of bikes I carry such as youth 20", road bike with skinny tire, mountain bikes with wide tires and medium width tires as well as a hard tail bike built for dirt jumping. All the different sizes mean some bikes may fit snug and some may be loose depending on the width of the wheel opening. You could make different size slots for different bikes though. Or if you just run one bike or the same tire on all of your bikes make them all the same size.
Either way if you build it, post up some pics and share your dimensions.