Shangri la Rasa at sentosa? I went there before and it can get humid, depending in the weather. If it rained the ground will be soft n muddy. Also saw peacock poop lol. Gotta consider that if the dining area will be outdoors too, the buffet area isn't sheltered so if leaves fall they will get into your food. We had ours at amara sanctuary, rom at glass pavilion. It's perfect for us because he wanted garden wedding and I needed air con as I sweat easily, so we got the best of both worlds. Our friends and relatives loved the food too. Oh, and the buffet line is just at the kitchen so refills are definitely fresher. Out of your options, I'd go with raffles. More convenient for transport too.