so I have this city/ruins I have in mind/need to make and I would like to request help from others who would know better them me. 

I need to set up a small section of the city for humans. the remaining would be taken over by warring factions of kobolds and goblins. 

There are massive physical barriers separating the city and keeping the really nice human neighborhoods apart from the other two.  The humans are mostly lawful evil, using the kobolds as one step above slave labor and pitting them against the goblins so that they never turn on the humans.  The kobolds are mostly employed in menial labor that the humans aren't interested in, working in entry-level factory jobs, domestic service, elder care, etc.  The goblins are there because the humans want the kobolds to see there is always someone interested in taking their jobs and desperate enough to do them for less.  This inspires the kobolds to kill goblins and the goblins to attack back in revenge and the humans to congratulate themselves on how much more civilized they are than the 'lower orders.'