What's your thoughts about covering the entire top of an outside aviary or only covering it half way. I'd like to allow natural sunlight in but I'm concerned about wild bird droppings and such.

My outside aviaries are covered about 1/3 but I do not have any migratory birds except a few swallow (european visitors) and have no predator birds like hawks.
We have owl but they are nocturnal when my birds are safely asleep in nestboxes. I dont think a bit of droppings of permanent bird residents matter that much, and we do clean the aviaries very well. My birds dont spend a lot of time on the floor so contamination risk is way less than the benefits of sunlight. Also there is no chance of the food being in any way accessable to attract wild birds. I dont recall ever seeing wild bird droppings in my aviary, possibly the birds are too loud to allow the doves to be comfortable. Doves and other small birds do visit the chicken cage to share food, I also leave second hand bird food out for the wild birds in other areas of the garden. Maybe you have to look at residents in your garden before deciding what is best for you.

My aviary is completely covered from above. I believe that the ambient light is PLEANTY and as the sun comes down far enough they get some direct sun in the afternoon for just a little while... mine tend to act uncomfortable in direct sun after a short while, so I carefully monitor the sun position, especially for Red.

The aviary is actually underneath a second floor deck, so I have no extra "celing" to deal with.