Invest in mosquito screens.
It's an ultra fine metal mesh that allows light & air through, but not much else. Even rain water tends to be diverted by being unable to stand against the mesh long enough to soak through. Get screens made for the outsides of the windows, then you can open them to let in everything while keeping the birds & bugs at bay. Get a larger version installed to the outside of the doors, called a "screen door" here in the States for obvious reasons, and your inward opening exterior doors can be opened in the same fashion as the windows. If your exterior doors open outward (towards the outside of the building), then you wind up with an interior screen door, having to open it to open the outer, and that's just silly.
Window screens & screen doors allow you to open the place up to reap the benefits of the world outside, all without having to let in the birds, bugs, & strays that might wander past. As an added benefit, if you attach a set of aligator clips to the metal mesh, a pair of leads to a switch, & then a power source, you're then in possession of some rather amusing form of solicitor repellent. Happy zapping! =-D