Others probably disagree with me on this, but in construct the only "hard" thing to make in a rts is enemy AI.
Its actualy got to be one of the most complex AI systems for any game. having to behave almost identical to the player useing the same objects.
and arguably no game has done a "good" job of making a challenging ai without cheating.
oh and you can't really use tile map's like every 2d rts you've probably ever played without a nightmare of rendering tiles but preserving edges for path finding.
so you'll have to build it with that limitation in mind.
and in-game menus are a pain, but that's true for any game in construct.
was actually thinking about releasing a series of tutorials on how to make a rts after i finish my next project.