MySql: how to get the desired result

I've a table like this:

CREATE TABLE `base_build_floor` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `build_no` varchar(64) NOT NULL,
  `build_name` varchar(64) DEFAULT NULL,
  `floor_no` varchar(64) DEFAULT NULL,
  `floor_name` varchar(64) DEFAULT NULL,
  PRIMARY KEY (`id`)
)

and insert some data:

INSERT INTO `base_build_floor` VALUES ('41', 'BUILD40210011', 'A', null, null);
INSERT INTO `base_build_floor` VALUES ('42', 'BUILD40210012', 'B', null, null);
INSERT INTO `base_build_floor` VALUES ('43', 'BUILD40210013', 'C', null, null);
INSERT INTO `base_build_floor` VALUES ('44', 'BUILD40210013', 'C', 'FLOOR40210002', 'C1');
INSERT INTO `base_build_floor` VALUES ('45', 'BUILD40210013', 'C', 'FLOOR40210003', 'C2');
INSERT INTO `base_build_floor` VALUES ('46', 'BUILD40210012', 'B', 'FLOOR40210004', 'B1');

the table is about a build-floor table, first you should make a building, then, a building can has no or some floors. the A building has no floor, the B building has one floor named B1, the C building has two floors named C1 and C2, I want to get the result as below:

41 BUILD40210011 A null null
44 BUILD40210013 C FLOOR40210002 C1
45 BUILD40210013 C FLOOR40210003 C2
46 BUILD40210012 B FLOOR40210004 B1

it means that, if a building has no floors, then get it, while if a building has any one floor, the building itself should not be got, so how to write the mysql?I've tried to use Subquery but doesn't work

I've try like this :

SELECT
    b.*
FROM
    base_build_floor b
WHERE
    b.floor_no IS NOT NULL
OR (
    b.floor_no IS NULL
    AND b.build_no NOT IN (
        SELECT
            GROUP_CONCAT(nostr)
        FROM
            (
            SELECT
                concat("'", f.build_no, "'") as nostr
            FROM
                base_build_floor f
            WHERE
                f.floor_no IS NOT NULL
            GROUP BY
                f.build_no
        ) t
)

)

but I get all the data