As of right now, you can only upgrade 1 building at a time.
This is tedious. Especially considering how long it takes to build once you reach anything over level 10. Taking your base from 12 to 13 is 52 HOURS.
So basically for 2+ days, I will basically just be occupying territory and that is boring. And makes me just want to put the game down. I'm sure you have had many players hit that time wall, probably much sooner, put the game down, and then their interest is focused on a different game /activity and they have moved on.
I don't see your metrics, but I know freemium games. If your players hit a point where they have to wait long periods of time and are not interacting with the game regularly, you lose potentially future paying customers.
The upgrade building que should be as high as your marching slots.
Level 1-5 has 1 building que slot
Level 6-10 has 2 building que slots
Level 11-15 has 3 building que slots
etc.
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If you don't want to tie them to Headquarters levels, you should at the very least, make them purchasable, to a maximum of 3 or 4 slots. We don't want people with 20 building slots. But I would pay for an extra building slot or two if they were permanent. I think fair monetary value would be: (Diamonds would be for your hardcore FTP playerbase. You don't want to alienate them.)
Slot 1 - Free (comes with game)
Slot 2 -$5.00 USD (or 1000 diamonds)
Slot 3 -$7.50 USD (1200 diamonds)
Slot 4 -$9.99 USD (1500 diamonds)
Or you could do "Rental Slots" for 30 days:
Slot 1 - Free (comes with game)
Slot 2 -$0.99 USD (250 diamonds)
Slot 3 -$1.49 USD (350 diamonds)
Slot 4 -$2.99 USD (500 diamonds)
I think that by doing this, it would support the game monetarily and give the players more control over their play time and experience within the game.
Thoughts?