You get free boots at 10 min. but you cannot buy boots before then. These boots give additional MS. For each takedown you acquire the boots 30s sooner.
Offense
+1-10% CDR
Flex
+6 Armor
Defense
+15-90 Health
WhyAftershock
Aftershock on Shen support makes him an incredibly strong threat in 2v2 lane fights where you're able to land your [E].
The bonus explosion damage, resists, and [Q] empowered autos make Shen a high damage version of Alistar.
WhyShield Bash
Shield Bash on Shen is easily proccable with [Q] and synergizes with his wanting to auto attack for the majority of his offensive damage.
WhySecond Wind
Second Wind doubles down on Shen's lane skirmishing. The mid-fight health sustain paired with your passive shield makes Shen difficult to lose a trade when a taunt is successfully landed.
WhyOvergrowth
Overgrowth's potential massive health scaling synergizes well with Shen's health ratios on passive shield and [E] damage.
WhyFuture’s Market
Future's Market on supports allows you to hit early game item powerspikes that much sooner on your limited gold income.
WhyMagical Footwear
Magical Footwear is a great rune choice on just about any champion largely for its raw gold value with no input. Think of it as effectively gaining a kill's worth of gold at 10min.