What? Seriously? 40% CDR is mandatory in any serious build on just about anyone who's not an ADC or an energy user. This is especially true on champions that provide more utility than anything else for their team. Having a Sejuani ult every 70 seconds instead of 120 is _massive_. Especially on SR coming out of the jungle. Just being unkillable will not win you fights as a tank, I mean, it's great and all that you don't die, but if you dont have the damage or utility throughout the fight consistently (ie. not waiting on cooldowns 10s out of every 12), you're much more useless than the guy built full tanky CDR with magic pen.
Being a tank is great and all, but if you can't give the enemy team a reason to attack your 4.5k hp, 250 armor, 200 mr self, you're useless to your team. Whether that's from damage or 1 second stuns every 5 seconds or a combination of the 2, just building pure tank is generally more detrimental than building tanky damage in most cases.
Oh, and items to stay away from in the jungle unless you're massively ahead due to cost:
Trinity Force, Sunfire Cape, Rod of Ages, ADC-type items, Needlessly Large Rod items.
If you're an AP jungler sorc shoes, haunting guise and abyssal scepter (in other words, magic pen) are your best bets for damage
If you're AD, Brutalizer and Hexdrinker makes for a lot of damage while you build tank items the rest of the time.