I hear ya on function over form.....luckily I live where form is not a priority.
Shade, sunlight, and air flow are all important....prevailing winds can play a part in designing a coop and it's windows and ventilation.
Could you build the ivy wall supported on a trellis set back from the deck/coop?
Ivy can become destructively invasive upon a structure....it can also grow rather slowly, so another plant might be more fitting for quicker coverage.
There are reasons why one must go slow and ask questions! Measure twice cut once comes to mind. When you said trellis I immediately knew what I should do!
Instead of ivy I will use vinyl lattice. This will provide better ventilation and is washable. This provides a bit of "decorative" privacy and I won't have to water it! LOLL
Again nothing is to scale.