See this:

https://www.militaryfactory.com/aircraft/compare-aircraft-results.php?aircraft1=1177&aircraft2=23

Used 747 as AWAC .. and even if it is smaller as an aircraft to what the actual AWAC is likely to be (a bit), in comparison to F35, there is still a vast difference.

In engineering terms you wouldn't use a sledge-hammer instead of fly-swatter i.e. why use vast resources to over-build the shelter? The cost difference is .. quite substantial.