How to make a RF Choke?
Since coil winding data is not provided for L2 the obvious solution is to just buy one. But if you insist on making your own...    

According to this site, it should be made from 26 turns of 30 gauge enameled magnet wire, close-wound around an 8mm nonmetallic (ie. "air core") cylindrical form.




Now let's see if we can figure out the inductance of this coil. We will use an approximation of Harold Wheeler's formula for the inductance of a single layer air core solenoid:-

L (uH) = r^2 * n^2 / (9 * r + 10 * l)

where r = coil radius in inches, l = coil length in inches, and n = number of turns.

But we don't know the length! However we do know that it is 26 times the diameter of a single wire. Bare 30AWG wire has a diameter of 0.01 inches, but enameling may add 10~20% depending on the type of coating. Assuming the coating increases diameter to 0.012 inches, the coil should be about 0.312 inches long.              

Now convert the form diameter of 8mm to inches, add wire thickness to get coil diameter (0.327 inches), plug all the numbers into a calculator and what do we get? 3.9uH! Seems a bit low, but apparently the circuits works with this value. 

Next: how to make your own capacitors, resistors, semiconductors...