You can build any mech in the Store. Click on the yellow Store button at the top in-game. Then,click on a mech and at bottom you will see View in Mechlab button. Click on it. You can build the mech to your heart's content even if you don't have the Cbills and you won't be able to save it, but you can still build it.
Edited by Coolant, 13 December 2015 - 12:19 PM.