Well, the only "list" about indoor rides in RCT that i found are from the "RCT-Wikia"
http://rct.wikia.com/wiki/Indoor_Ride
It's only about RCT 1-2 but most attractions are the same in RCT3, sometimes with different names but the type is the same.
I think that Atari dont creates a completly new code for the rides in RCT3, so if they used the original one than the list from RCT 1-2 could work with RCT3, too.
Than i found an thread that shows, that the ingame roofs in RCT3 are only for deco, so the are not for build a rainproofed flatride.
A big differents to RCT2, because in RCT2 its possible to become rainproofed rides if we build Scenary-roof/floor above the ride.
http://www.gog.com/forum/rollercoaster_t...s_and_rain
And it shows that "indoor" rides aren't rainproofed coded in RCT3, like 3D-Cinema and others. Another bad thing in RCT3, because in RCT1 and 2 the rides had two classifications: indoor and outdoor.
It seems that RCT3 has only outdoor rides as classification (really realistic from Atari, nice Job)
So i think your search could be over, because "NO" single ride in RCT3 can be build rainproofed!
If the rain comes, pray and hope for the best (if you play the campaign/scenarios).
Sry for this bad news about it, but thats the only things i found out.
I haven't experience by my own about it, in fact that i've never played RCT3 for campaign/scenarios infact that RCT3 is totally crap without CSO's.
Only the sandbox mode with alot of CSO's are my personal reason to play RCT3, and there for me it doesn't matter if my peeps ride the flatrides or not.
They are only deco and give some atmosphere to my Coasters, not more or less.
Lg Cheleste