In addition to landlord's approval and confirmatory votation from neighbors in the building and adjacent buildings, you will need to ensure that the cats that roam the area will not suffer from ingesting the little birdies (have the composition of the bird food AND the pre-existing content of their gizzard professionnaly tested and post the results of the analysis at the Gemeindehaus for AT LEAST 21 days prior to the provision of food).
The bird shed will need a building permit. Again, the Gemeinde Buildings Dpt will help with this. Ensure that the building materials come from renewable source, preferably alpine forests. Style of the construction will depend on the architectural character of the neighborhood AND the orientation towards the sun (and full moon in case of eclipse).
There is no longer a requirement to have an anti-nuclear bunker associated with the bird shed (this is 2012 new), although new anti-sismic regulations are under consideration. Check with the Gemeinde.
This is all I can think of now. I do not give tax advice, hence cannot advise on whether you will be taxed on the virtual rental value of the bird shed.
Good luck.
We can go on actually (thanks Sbrinz for bringing up the poo factor) - so many things to think about :
1. disposal or (better !) recycling of bird droppings. Container, day of the week, precautions
2. NOISE - those things chirp
3. RATS - they love bird food. RACOONS. BEARS coming down from parched woods in search of food.
4. your entry here