@Sage Chow: It's what I've done, they're very effective timers... oh, and you can use... TIMERS! Use 'Custom Script: if GetExpiredTimer() = ... then'.
@Wraithling: Here comes the review... For the sake of the review, I will review it like a do a map.
Presentation - 3/5 - Meh. Aside from that bug posted by Zpider, there were alot of other things that could be improved.
-Names
'Flying Structure Prototype'? How about Sky Galleon, Atmos Barge?
This is just an example. There are some other names that need some more originality. eg. the Steampunk tower and lab, Chariot, and wtf is a Tech Shooter? I think you could've changed it to something like 'Grand Marksman'.
-Icons
Meh, bit bland. Could have used some different icons for the different Solidarity abilities. However, most of them were good.
-Models/Skins
I liked the hero models, and I know that it is hard to find a steampunk-type robot model, so I won't criticize the Junk Collector. However, I disliked most of the aerial models, with the exception of the 'FSP'.
The above is completely my opinion, thus it is not as reliable and not objective.
Gameplay - 4/5 - Hey, hey, the good bit! Generally flavoursome.
-Solidarity
Awesome sauce. However, your use of them could have been better. Like I said, the different versions of it could've used some different icons (imo), and the effects weren't as interesting as expected. I would give it a more exotic, yet balanced and useful effect. eg. instead of an Armor bonus, the Guardsman may have a Parry bonus, which % stuns and knocks backs enemies who attack any unit with the buff. The % and distance/duration could increase per stack.
-Recycle + Lumber
The Recycle was a very simple, yet effective system. However, I think there ought to be a better way to gain lumber. With the current system, it relies on your Junk Collector and constantly wasting gold to buy lumber, which btw decreases the gain rate per Market. And I didn't get to test it, but I think Recycle should only work for mechanicals.
-Misc
Since you're the 'Air Humans', maybe you should nerf an aerial unit and include it in Tier 1. Perhaps just as a scout or something with no attack, so it isn't OP.
Balance - 2/5 - This is the bad bit.
-Mechanics
As said, I think the lumber 'gainage' method is imba. The Solidarity and Recycle mechanics are unique, but they set it apart from the other 4 races too much. Now, I'd have no problem if you were making your own map and all the other races were equally balanced, but as of now the Air Humans are so unique, they're unbalanced (this only applies to your current race, this isn't a general term to say 'similar is smarter'). Resource management especially, has too much ups, downs and complications.
-Units/Buildings
I didn't like it. The fact that you have only 8 units (not including upgrades/morphs etc.) and 3 heroes makes it badly UP. If you somehow managed to keep them balanced (I'd say through combination, rather than individually), it'd work. BUT, you're strongest unit is the FSP and it doesn't attack. The rest has below 600HP, and their attacks don't exactly pack a punch. You may argue that Solidarity compensates, but, from the start, it was always supposed to be a support mechanic. So, you're left with a bunch of units with little to no firepower and crap defense.
Along with this is the lack of a 4th hero. It wouldn't be so bad if you managed to pimp your units, but the reduced amount of heroes just compliments your balance.
Bases were prone to attacks easily. Their funkin' Town Hall is weaker than a Barracks!!! If you managed a work-around, like the NE's HP regen and Root ability to compensate for their buildings' weakness, that would be alright. But, I see no Call To Arms, no Spiked Barricades, no attack with Frost effect, and definitely no Root. You again, could argue back, stating its low cost, but, that's a benefit among many weaknesses. Yes, you will use considerably less resources, BUT it is incredibly vulnerable for a Town Hall, especially considering its 120 sec build time, This makes it take considerably long for a TH that supsceptible to attacks, hard to defend a large attack on your base, and impossible to claim a new Gold Mine mid to late-game.
And come on, if you're gonna make a tower require a garrison, AT LEAST make it worth wasting 1 worker (and 1 food). Its attack is very low, its attack rate is low, and its HP doesn't make up for how it is a sitting duck whilst your Workswomen are busy in the Gold Mines.
One last thing, what happened to the 'air'? You could've easily tried to give the Air Humans more 'air', other than giving them some more flyers (half of which are made from upgrades and mounts). Refer to what I said, a Tier 1 flyer. This is just an example, but you could've implemented an Airship unit similar to the Zeppelin, that's adept at going in and out of combat. I believe you also said they were sorta nomadic. Where'd that go? There are many ways to do this (not including the NE's Root). Just a faster Build Time would emphasise it.
Of now, I see this as a race with little attention to its units, supreme focus on resource management, and a half-empty effort at making the Air Humans, 'Air' (you never had any mechanics to supplement this, and 4 flyers and 3 bonus flyers don't make up for it).
Creativity - 4/5 - Back to another good point, the Air Humans are a creative race. Most Steampunk races focus on mechs and dwarven shit. This, puts a unique emphasis on Aerial warfare. I only wish the implementation was done better. The Mechanics are very good, and so too are the units. But, I believe you let this get in the way of balancing.
Storyline - N/A
Triggers - 4/5 - For a race which uses so many custom abilities, with a lot of triggers, it has little to no lag! The triggers were nicely done, and I won't penalise just because of that reveal shit. Btw, alongside Zpider's solution, Mephestrial has made a template with his triggers a few pages back.
Overall - 17/25 = 3.4/5 = [3/5] - The concept, the idea, the inspiration, all good and well-meant. The execution, the implementation, not so much. I agree with Zpider that this race is handicapped big time, compared to the melee races. To sum up, your ideas looked good on paper (especially Solidarity), but it just doesn't work.
This is my opinion, I'm not a judge, you don't have to give a shit about this post. Good luck
EDIT: This is NOT a giant criticism to your submission. I prefer to point out more bad points, as that's more useful.