Possible to build a 10 disc duplicator?

Yes you can do this, but depending on what you are doing it for, you may have better luck with products made for the task. My job requires some serious disc duplicating, at my work we use products from Microboards. They are pricey, but their support is very good. We have duplicators from 3 years ago still going strong, and when drives die, they can be replaced by Microboards. I have a number of things from them, including a 5 xBR ESata tower, (uses 1 esata port) and 8 10x BR towers, which are standalones that can be daisy chained to each other. They usually perform at about 98% without failure, which is really good for us.

When we tried to make a tower to save money, we did not get a single run when connected to 10 BR-R drives to complete without a disc being bad. We had used RAID 0 for the HDDs, because you need throuput for trying to burn 10 x DL BRs at a time. As well, the opticals were added using onboard SATA and 2 4x sata controller cards.

One other suggestion, use quality media for the drives, it makes a big difference. Each drive model it seems has its own particular brand and disc that works best, try out a lot of each brand and model before buying bulk.