4 layer buck converter layout
An unbroken ground plane on layer 3 or layer 2 is good, but don't let it lull you into a false sense of security.
The most important thing with those 'noisy' components is to arrange them so that the loop area enclosed by the changing current paths is as small is possible. Paradoxically this means that the tracks to the inductor are not the most critical, as the current through them does not change abruptly. It's the varying route through the switching device and freewheel diode that are critical.
As the switching device goes to ground, resist the temptation to simply connect it to the ground plane in some random place, connect it so that the loop area from it to the ground connection of the output filter capacitor (the place where the alternate current ends up) is as small as possible.
Once you've take care of those radiating loops, just simple tidiness will allow you to make use of all those layers to route the rest of the design. There's little need to have a VCC plane, it's just a waste of space on most designs. Make sure the tracks that take the input and output current are wide enough. Flood-filling all the layers will maximise the thermal conductivity of the board. It's usually good practice to ground those fills, not least because the vias add additional Z axis thermal conductivity.