I'm looking into buying a new Mac mini. I would like it to have Fusion Drive. Apple charges out the _ss for it, but I was wondering how hard would it be to make a Fusion Drive myself? 
Is it worth saving $75 (and taking the risk of screwing up) over ordering the mini with a 128GB/1TB fusion drive preinstalled?
In addition to checking that you have the technical skills to do this upgrade make sure you price out the cost of doing the work yourself. It will cost you $175 to add a 120GB SSD from OWC (with Data Doubler kit). Is it worth saving $75 (and taking the risk of screwing up) over ordering the mini with a 128GB/1TB fusion drive preinstalled?
It wasn't for me, plus I wanted AppleCare and didn't want to have to undo the DIY install if the Mac ever needs service. I think the factory Fusion option is well worth the price.