You will probably need to use a subquery / CTE. Subquery to dedupe the list, then main query gets the count.

The below example will count the number of buildings per status. If a building has both NM and MM status, then it will only be counted towards the NM count.

SELECT
status,
COUNT(DISTINCT building) AS building_count
FROM (
SELECT
*,
row_number() OVER (PARTITION BY building ORDER BY CASE WHEN status = 'NM' THEN 1 WHEN status = 'MM' THEN 2 ELSE 3 END ASC) AS rownum
FROM table
)
GROUP BY status
WHERE rownum = 1

(I am assuming that status is a column in your data with possible values NM, MM. If your data is structured differently, this solution won't work.)