Buck - Boost converter inductor selection
Inductor selection is based on a few things. Higher inductance leads to lower ripple current which leads to lower ripple voltage (through ESR of output cap). There is also core material (although this applies moreso to winding your own). Different core materials have different properties. As you put more current through an inductor the permeability goes down which makes inductance go down. The same can be said for increasing your switching frequency. 

Anyway, there are a lot of ways of calculating the required inductance, but they all boil down to Vl = L*di/dt. In designs such as this you can use: L = (Vout * D * (1-D))/(deltaI * Fsw)

Where D is your maximum duty cycle, deltaI is your maximum allowable ripple current (usually 20% to 40% of Iout) and Fsw is your switching frequency.