A lot depends on how tame your sheep are. We started out with
Mad Manx Loaghtans, who took the word 'hurdle' quite literally, so we ended up building
a substantial handling pen for them (yes, total overkill, but money well spent in that it's one of those things that just works, and will last a lifetime).

Then we switched breed to Zwartbles, and really we'd be fine with just hurdles these days as they're so much more biddable. A bucket of nuts is also much cheaper than a collie! We still use the pen though, and seeing as I'm starting to have back trouble, I'm now on the lookout for a 2nd hand turnover crate to add to it.
As Tim says, what do you want to achieve with your system? Shedding into different pens or fields? A race for dosing? Weighing? F
oot bathing? Foot trimming? Dagging? Also do you need to be able to operate everything on your own, or will you have help? Once you know the answer to these, I reckon you'll be well on the way to knowing what to do.