You can check out Singapore Carpentry. Their IDs are good and there's also a pricing calculator for their carpentry services on their website, which I've found quite helpful! http://www.carpentry.sg/pricing
Did you manage to find a contact? I'm thinking of doing the same thing and found this link helpful, but I think I might still get an ID to do it. http://www.instructables.com/id/Low-Cost-Indoor-Pond/