Terrain Building
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d4d6d8d10d12d20 there are some ideas for creating your own terrain projects (current have a video series of creating your own water tiles for similar to the dwarven forge for cheap) and some other papercraft templates and freebies.
Overall look into papercraft products, once built they are pretty durable if you store them correctly, and if you use foam core for the base you'll have plenty of durable game terrain (similar to dungeon tiles)
Initially I also looked at the hirts arts products and was in wonderment of what you could build for your campaigns. The only drawback I saw was the initial investment, and decided to construct some of my own molds.
I'd say the easy route is just to pony up and get hirst arts molds most of his stuff is designed in a way to worth with most of his other molds without too much effort. I spent a month straight of working on clay models of "stone work bricks and bases" to cast my own tiles/bricks and i'm still not 100% happy though 85% is more accurate. Also the stuff is "heavy" to transport around.
The one thing that you've got to know about the "build your own models brick by brick" hobby is that casting your bricks and then building them takes a lot of time even if you have a "system" down. Think of it exactly like legos, building small things fast is pretty easy doing elaborate buildings will take a while, and unlike legos those bricks don't "interlock" you've got to glue em together. (btw I used quick casting resin which cut down time, but then you have to wash the demolding agent or paint won't hold, and I found that most glues don't adhere well quickly to resin so i used locktite gel supergul which worked great on resin casts, which i did a write up of the various adheasives you can find and put it up on my blog
d4d6d8d10d12d20)
Also making your own mold will be somewhat pricy too depening on what silicone you use (which is really the only thing you should use to get some nice detail) tin based silicone is less expensive, and platinum is of course more expensive but worth the price as its more durrable and typically you can get it in one to one mix ratios which is important. (tin usually is a 1 to 10 ratio so its kind of a pain to use)
Again I would suggest you go with a hybrid of dungeon tiles (you can make them with foam core and google images really of stone floors, etc.) and paper craft products with a smattering of railroad trees (which you can make too on the cheap) with a small subset of these tools you can set up almost any encounter, then if you know what the group is coming up against say a chess floor with some weird runes on it, you can quickly customize a new piece that fits in perfect with your old terrain items.
anyways, I'll think i'll start a write up on my blog regarding the process I did when I was making my own tiles, soon since I've had a few requests of the same nature as your original and I took pictures as I went along too so I have the content just have to put words to paper, so to speak.
-david c.
d4d6d8d10d12d20 - my game blog