Neighbour parapet over my boundary wall

Hello,

Resolve your dispute with mutual and amicable settlement as he is your neighbor. Alternatively, you may send a legal notice as it is blocking your ventilation. 

Normally the setback distance is calculated from the boundary to the building wall, and the projection of the sunshade is not considered in the calculation. But no part of the construction or even trees can't cross beyond their boundary line to neighbors' plot. So, if the parapet is over your boundary wall, I assume the boundary wall is inside your plot, you can file a complaint with municipal authorities or even in court to get the projected part of the sunshade demolished which will force them to come to you for an amicable settlement.