step up transformer on mosfet source follower ?

I am trying to figure out the calculations for a 1:20 step up transformer on a mosfet source follower.

i don't have any specific details other than how do i determine minimum primary inductance of it? it is based on impedance of mosfet correct?

I am unsure of primary current either... maybe 100mA dc. max dc voltage of 20-30v.