I think 18/18 is a weak build for a shielder. You have two options:
- Going for an agi shielder. (15/21, 12/24, 9/27)
- Going for a str shielder. (21/15, 24/15)
If you go for a agi shielder.. you're forced to take blunt/pierce weapons. Otherwise, you will glance a lot and will need a lot of hits to kill a armored guy. Str shielders must have a long range weapon, like long eslavona, elite scimitar, scimitar, or knightly/nordic. 140wpf for a shielder is more than enough. Unexperienced shielders shouldn't go for an agi build because you will pay for your mistakes so hard. Agi builds allow a shielder to fight multiple oponents, but lack of hitpoints. 21/15 with 7 ironflesh is the easiest way to start. 5 points in shield skill is enough. Breaking a huscarl is not an easy task. You have to avoid weapons with bonus vs shields.
I think 21/15 with heirloomed gloves/armor is the best build, or at least, the most balanced one. 70 armored hit points let you survive in a battle, and surviving mean that you will make a lot of kills (guaranteed). 24/15 is a awesome build if you know how to play. Just get medium armor and a high dmg/reach 1h weapon.
Another suggestion for shielders. You MUST have an axe as sidearm to fight another shielders. One handed axe is enough (cheap). If your shield is broke, you're dead.
Each player have his own style, but shielders even more that other classes, need powerstrike unless you're going for a steel pick shielder.