Does anybody know how to create custom animated flags for rct3? Ive got sketchup and the importer and the sketchup plugins.

I don't know how, but I do know there are a couple sets of flags in the download section, maybe you could pm the user that created those

Elmer BeFuddled, the creator of these animated flags as well as others, claims that this website is where he originally obtained the flag animations, possibly from the Animated Flag Gif tag.

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Alternatively you can use animated billboard flags.

For example:

http://rctgo.com/downloads/view/10343