"In the city you will find more houses than trees."
Translation:En la urbo vi trovos pli da domoj ol da arboj.
I think your sentence does work, in that your "pli" relates more to the verb "trovos". It's rather like saying "You will more [often] find houses than trees".
Perhaps this could be compared with a sentence in PMEG: "Mieno lia montris pli suferon, sed ne koleron." (http://bertilow.com/pmeg/gramatiko/e-vortecaj_vortetoj/ceteraj/pli_plej.html)