The phrase "missing shingles" means that some parts of a roof are not covered with the flat pieces of material called shingles, which can lead to leaks or other damage. Full definition
Inspect your roof for missing shingles and possible leaks and do any repair work if necessary. (armourinsurance.ca)
Evidence showed that the lack of completed repairs was obvious to the homebuyer and her husband during the inspection as there were missing shingles on the roof and peeling trim. (nar.realtor)
A few missing shingles, a piece of metal stuck on a roof, a downed fence. (usatoday.com)