It's true that you can make your own multi-tip system if you so desired. I for one do not particularly like to cast T-14 or LC-13. I don't enjoy the "chuck and duck" type of flycasting.
But considering that an 8wt RIO Versitip costs about $169 retail, it might be a better deal than a homemade one utilizing RIO tips. I break down the costs as follows:
1) Basic good quality full floating line to provide the belly and running line for the system: $49-69.
2) Four 15' RIO tips (since the full RIO system provides 5 tips) at $19 each: $76.
3) Add your time and labour for cutting the line and forming the loops...add around $20 if you are going to buy and use braided loops.
In the end, you would spend between $145-165, plus your time and the risk of cutting the floating line in the wrong place...and you could have bought a well made factory tip system for only a few dollars more. Granted...if you do use the T-14 or LC-13 for tips instead of RIO tips, you will save a lot of money. But like I've said, it just depends on what you expect out of it, and whether or not you would like to enjoy casting that line or not.
If you do buy an 8wt RIO system, you can save money by re-using those same tips for an 8wt spey setup later. I've recently bought another spey outfit to compliment my 9140. I've picked up a 7wt spey system, and I bought an Airflo Delta Spey floating line for it. Rick Baerg at Fred's Custom Tackle cut back the front of my line and formed a pretty cool loop using the core of the line. I'm going to be using the sinking tips from my RIO Versitip 8wt with that line tomorrow. Having those heads saved me a bunch of money on my spey setup...and both lines will cast very well. Good luck!