*Quick Note* still revising the guide every day so keep looking for updates.
Just what you think it would be, Squishy destroyer and even more of a pain in the *** to kill. When all said in done with stacks on leviathan you have 5k hp and around 300 AD. I would suggest starting off with a health crystal to be able to up to a leviathan early on and start ganking lanes to get those stacks right as soon as your level 6.
I of course base started this with going two sunfires but that seemed to limit too much with the atma's so I picked up a warmogs and atma's instead and the build has over all been... well better.
*Edit* I have not been on in a great deal of time as you can tell since I reference "Two Sunfires" I have had a decent amount of requests asking me to expand the build from the comments and from other people that I play with, so here it is....
I take Greater Mark of Resilience for the added armor, Greater Seal of Evasion for the added dodge and Greater Glyph of shielding for the added MR. Quintessence of Evasion is my main quints I like to use. But I have also used Greater Quintessence of Swiftness for the extra movement as it adds a even better chase/evasion mechanic to a character that already excels at doing so.
Alternate Runes can be added as you explore playing Nidalee as a tank.