Septimus39 said:
Can you make a chiller or a filter or a light fixture? .
I agree that a chiller is not practical. You can't use a window shaker unit-not enough BTUs. The unit you would need would be too loud and not be very effective.
Cephs don't have any real light requirements-except not much of it. You could use the buzzing shop lights that are only $10, but a simple ballast light is much better and easier to live with.
Filters you can DIY all day long. You have to buy the pump, but a trickle filter is easy and handles a large bio load. Reef Central has alot for filters, but current reef philosophy does not believe in Wet/dry filters. I disagree for cephs. Wet/drys are easy, cheap, and effective. Don't buy bio balls, I even heard someone on this site refering to plastic army men -which would work just fine. I bought the balls to save the most space, but army men would work too, inert, with lots of surface area.
A simple counter current skimmer is doable, but it would have to be big to let the bubbles have enough pull on the water flow for a octo.
Simplest thing is to go small, 30-40 gallons. Get good used equipment from yard sales and ebay. DIY a big filter and get a good skimmer on ebay- get a bimac or bandensis when everything is well cycled and matured.
Have fun making and planning it, and be protect the animal to enjoy him as long as you can. If you don't plan well it will just be a frustrating experience.
Just my 2 cents.