Nesting in my roof

Hi all, I apologize in advance if this has been covered many times in the past but I have just joined the forum this morning because I have a problem with nesting in my roof but want to do the right thing. Since moving into my house 3 years ago we have had a regular nesting issue in the roof. There is a design/building fault on the roof that has left gaps on the corner of the gable ends and birds are regularly in and out. In the front above our bedroom we notice the rustling, chirping and flapping starting around this time of year (April/May) and it will go on throughout the summer. But at the back of the house we notice the same noises all year round - I get up at 5am for work and dress in the spare room and regularly hear them in the winter when its cold and dark. Is this likely to be a bird that's nesting all year round, or could it be bats? We do notice them flying around in the lighter evenings. As much as I love wildlife the bird feces is becoming a big issue all around the house, on the house walls, on the car etc. Plus the noise keeping us awake is getting really bad. Can someone advise me what I may be dealing with, and how and when to deal with it? Many thanks in advance.