Looks like the card based system for selecting your structures is going to be a bit more involved than I initially expected.  I'm going to go learn how to do that, so it might be a few days before this next update.  The next update will occur when I have that basic system implemented as well as more build options.  The cards right now would really only be the three structures, the block, maybe the trap can come back, and the two base upgrades for really only 7.  Maybe add direct damage and repair cards of low and high strength for another four to make 11. Limit the hand size to 5 maybe?  I'm brainstorming as I'm typing I guess.