Also consider: *How big do you want it?
If you are using a small tank [10 gal for instance], that will put limits on what can go in it. Personally, while I REALLY think water features are cool, I feel they are best reserved for large tanks/terrs -- they require a lot of space.
*How much work do you want to put into it?
The more ambitious the project the more work it will be to set up and likely to maintain. [I know that is a 'no brainer' but it really is a point that is soooooo easy to forget about in the heat of the moment.] :)
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DH gave you a sensible starting point -- this forum, (including the FAQ). There's a lot to read here, I know, and TM gave you a ton more sites to check out. LOL If you have more specific items you can also use the search engine for this forum.
I also agree with TM that while there are some truly AWESOME setups out there, for your first terr keep it modest! It will help give you an idea of how much work is actually going to be involved, to see what works for you and doesn't, and to discover what is most appealing to you.
A couple other points you will see time and again but bear repeating:
1) Just about any clear container will do. Your imagination is the limit.
2) If you are even considering having animals in the terr please DO YOUR RESEARCH. Animals complicate matters many times over.
Don't be disappointed if this forum moves slowly at times. Problem seems to be that once folks have their terrs set up, there isn't often much to continue chatting about. Only so many terrs one can have ...
Keep us posted!
:)