For those of you who have yet to read the Defining the Roles topic in the General Discussion section of the forumns, I suggest you do so to better understand these topics.
I'd like to start out these posts with one of my favourite playing styles, which as the topic suggests, is the Heal Shield. This is a healer, usually a Cleric, that's customized to be great at both healing and tanking. However, this can make it difficult to do anything in your party other than be a support character, as your melee ability could suffer, and your Turning may be sub-par. When acting as a support character, though, your heals, buffs, and ability to survive will be amazingly powerful, even if you are forced to rely on others and lack a strong solo capability.
28 point build:
8-10 Str
10-12 Dex
14-16 Con
10-12 Int
16-18 Wis
8-10 Cha
The most important stats for a Heal Shield are Wisdom and Constitution. High Wisdom allows you to heal your allies more often, and moderate to high Constitution will help to keep you alive, especially later on. Strength really isn't that important as you'll be focusing on support, and Charisma really is only useful for Turn Undead. There are other means of killing undead as a Cleric, but if you really want to be good at Turning, cast Seek Eternal Rest on yourself to increase the DC. Intelligence is useful as a Heal Shield for the skills Healing and Concentration. Diplomacy is useful in some situations, but not if you're the primary tank in a group. 8-12 skill points at character generation is plenty as a lot of your skills are going to be suffering from -massive- armour check penalties. My level 7 Heal Shield has a -29 to Swimming, for example.
32 point build:
Same as a 28 point build, though you may want to bump up your Strength for -some- melee capability, or Dexterity if you plan on getting Mithral plate armour and take a few enhancements.
Class:
I recommend the Cleric for this role, as they are able to use Heavy Armour and shields without problem.
Skills:
Healing and Concentration will be great choices as a Heal Shield. Diplomacy is, again, optional and depends on whether you plan to tank all or just some of the time.
Feats:
Bullheaded can be useful if you put some points into Intimidate. Fighters will be better tanks than you will, though, if they specialize in it.
Combat Casting is a good choice to take if you don't put points into Concentration. +4 in that skill will help you to cast even while being swarmed.
Dodge is alright if you go with high Dexterity. +1 AC really won't help much later on.
Empower Healing Spell is a great choice that I high recommend taking at around level 9. This will actually lower the SP / HP recovered with higher level healing spells.
Extend Spell can be a good choice if you don't like having to recast buffs. It will double the length of your buffs for ten extra SP.
If you choose Halfling as your race, you may want to consider getting the Dragonmarks for a number of free healing spells per rest.
Mental Toughness and Improved Mental Toughness are, as usual, great feats to take. More SP means more healing after all.
I'm not sure if Improved Shield Bash allows you to retain your DR while bashing. -If- it does and you have some extra Str, I highly recommend taking this. If not, an extra two AC isn't going to help much later on.
Shield Mastery and Improved Shield Mastery may be good feats to take. Extra DR means you don't have to heal as often and are more likely to survive.
Maximize Spell is a good choice to take for fourth level and higher spells if you want to branch out as a combat caster. Note that other roles will be -much- better than you at this.
Mobile Spell Casting can be useful for those situations where you, or another member of the party, -has- to run away from a fight. Running while casting a healing spell can be useful for tactical retreats or getting around a dungeon quickly.
Quicken spell can be useful if there's a single spell that you absolutely need to cast multiple times in a row. For healing, just alternate between two different spells, such as a Cure Serious and a Cure Moderate, in order to constantly be healing.
Skill Focuses probably aren't good feats to take, even for that +3 to Healing. Far better to take feats that will be more useful in combat, like Improved Mental Toughness or Empowered Healing Spell.
For a bit of extra DR, consider taking the Tower Shield Proficiency feat. Tower Shields are the best tanking shields you can get, but you may want to trade this feat for something else later on. At low levels with this and a set of Adamantine Full Plate, you can easily achieve 12/- DR when blocking.
Enhancements:
Any improvements to SP, Wisdom, healing, Dexterity (to maximize your AC while wearing that Plate armour), or Constitution are great Enhancements to take. The Faith Enhancements can also be useful at lower levels. One or two Turning Enhancements will allow you to use those charges of Turning that probably aren't going to affect undead anyways.
Tips:
Remember that as a Heal Shield, your job will prettymuch be running into groups of enemies (when pulling isn't needed), blocking, and then healing. Keep a careful eye on the health of your party since they'll rely on you to keep them alive. Some things for your group to consider are that you can't heal anyone unless they're in line of sight and in range, you may not notice that big shiny chest that's overflowing with loot, and if you go with a Cleric, you won't have Intimidate so they should focus their attacks. I'd recommend this build to any healers that'd like to give tanking a try, and any race except for the Warforged as they won't be as effective at healing themselves.