Flat is for walls and ceilings, although I like Satin or Eggshell for walls. Semi-gloss is usually used for wood trim, doors, cabinets, etc. that have a lot of potential to get dirty or get fingerprints on them, etc. and where scrubbability is important. As for a Cabana, I'm not sure exactly what you would use to paint it.............I don't like flat because it attracts dirt like no other type of paint.