If it's anything like mine, then the roots will be very chunky and go on for miles! Back in May I planted my potted Cordy in the ground (it's pot was massive - prob about 2ft tall). When I moved it to get it out of the pot, the roots had grown up the inside of the pot and they were the chunkiest roots I've ever seen (on what I stupidly presumed 4 years ago was just a plant - now I'm a bit wiser and realise they grow to be humungous trees lol!). It should've gone in the ground a lot sooner, and thankfully it seems to be thriving so far.
Can I ask why you plan on potting it up, 3ft is a bit big for a pot (in my own opinion). If it's in the ground I would advise you to leave it there, it'll do much better there than being uprooted and plonked in a pot.

I'd imagine you want to pot it because you live in a part of the States that gets very cold over winter, and need to put it somewhere more sheltered? The roots shouldn't be too extensive, but start digging a foot out from the central stem, carefully loosening all round without breaking the roots. Best done with a garden fork, not spade. You'll need a large pot for it though/

And I would cut off the oldest 1/3-1/2 of the leaves, to reduce shock. If you put it indoors, be sure to give it plenty of sun.