To keep birds from nesting on your porch you can put up some reflective bird diverters at three or four locations around your porch hich will keep birds from landing on or going near your porch.
Also buying a fake plastic hawk on or near your porch will keep birds away since the fake hawk will scare the birds away so they won't want to land on your porch or come near your porch.
Another good option although I haven't tried it myself is to buy some of those plastic bird spikes and put them on your porch to keep the birds away.
I've seen them in Walmart for $14.00 and some people have said they work good for keeping the birds from nesting on their porches.
So you might want to give them a try.