• clubroom,
• clubbroom,
• clubrroom,
• cub-room,
• club roome,
• clubrooms,
• xlub room,
• vlub room,
• flub room,
• dlub room,
• ckub room,
• cpub room,
• coub room,
• clyb room,
• clhb room,
• cljb room,
• clib room,
• cl8b room,
• cl7b room,
• cluv room

The adjective form of "club room" would be "clubroom".

The plural form of "club room" is "club rooms"

The singular form of the word "club room" is "club room". The singular form remains the same as the plural form in this case.