You get 3 Slots to start with but you can buy more either with gems or by playing premium.
From what I understand you get 1 extra with Premium and then you can also buy another 3 with Gems
making a total of 7
So....What do you gain from that, the way I see it all you can do is queue 7 build orders.
Seems rather pointless to me and expensive waste of gems.
Or am I missing something?