Ciao Slasko,
there is a nice Berlevag Airport for msfs for as little as 7 euro you can get and idea on how they designed it
Flight Simulation Scenery
www.onfinal.dk
You are asking what is better, but better is just an opinion, in the 3d design world you are the artist, and you are the one who decides what is good, what better what is not, there is really not a right way of doing things
Anyways
Texture resolution, by itselft, means nothing, its the way you are using it !
You are talking about using a defined number of texture, so i presume you want to avoid repetition/tiling because you want later on importing it in substance painter (or any other material painting software) do add custom
scratch, dust, mud, moss and so on
Let's analyze the building, it is 100 meters long, 10 meters wide and 3/4 meters height
so you know that:
the roof size is 1000 (100x10) meters squared-10.000.000 square centimeters, a perfect unwrap with a 4k texture (that has 16milion pixel) will give you a REAL resolution of 1,6 pixels per centimeter
the sides are 400 (100x4) meters squared, that 4.000.000 square centimeters, so using a 4k texture per size will give you a real resolution of 4 pixel per centimeter
this is what you should aim for, a decent and more or less CONSISTENT real resolution
(also, remember that for each texture you will most likely want a normal map a ORM/COMP texture)
of course, you will want to add additional texture for signs/ air conditioners, and other small details like that
since i'm not a substance painter user, I prefer using smaller textures, tiling them, and adding details with decals, but thats my way of doing things