<Grief>
Complete Loot Rules for 25 Man Raids
TLDR!  I Have More DKP than the Top Roller:  How Much is it to Buyout the Item?
Your DKP -->
Top Roller's DKP -->
Base Cost of Item -->
Press to Calculate Item Cost -->
What the Item will Cost you to Buyout -->
Looting Procedure
1 - Using the bidder addon, players click the item(s) they want (for either main spec or off-spec) in the list that shows up when a boss or trash mob is looted.  
2 - For each individual item, main spec rolls will be called for first, followed by off-spec rolls if nobody chooses to roll for their main spec.  Players roll accordingly.
3 - Depending on the quality and demand for the item being considered, loot council may decide which players are eligible for the item being rolled on (to a varying extent as listed below).
4 - After any loot council intervention, DKP rules apply as normal to the item.
DKP Rules
1 - DKP is awarded at the beginning of each raid as an ontime bonus, then at 3-6 dkp per hour until the raid is called.  Officers may modify the value of DKP awarded on a given night based on raid performance (e.g. first kills on progression bosses, extremely good progress learning a fight, or poor performance overall).
2 - DKP is spent when awarded a main spec item based on the base cost as listed below, plus modifiers based on specific conditions.  Offspec items are free; these are not the same as minor upgrades/sidegrades.
3 - After any loot council intervention on a particular item, each player who has higher DKP than the top roller has the option to spend extra DKP to buy out the item.  The extra DKP spent is found by using this formula rounded to the nearest whole number:  ((Higher DKP Value*30%)-(Higher DKP Value-Top Roller's DKP))*(Rolled Item Cost/Top Item Cost For Patch). If this value is less than 1/2 the cost of the item, then 1/2 * the base cost of the item is used as the extra cost (this used to be 10 straight DKP points, but using percentages makes more sense in order to scale with the value of the item).  English Version: If your DKP is much higher than the top roller's, the item will cost less.  The opposite is true if your DKP is close to the top roller's:  it can wind up costing you as much as 30% of your total DKP to buy the item out.  If all higher in DKP pass or there is nobody higher, the top roller receives the item for its base cost.
Example Loot Scenario
Resto/Moonkin leather boots drop, best in slot (BiS), which have a base cost of 30 as per chart below.   Sakura rolls 12, Casie rolls 8, Doogiewoogie rolls 90, Moonblizzrd rolls 100. Loot council eliminates Moonblizzrd's roll due to drastic attendance or performance difference compared to the other rollers (more on this below).  Sakura's DKP is 340, Casie's is 225, Doogiewoogie's is 224. Sakura's cost to buyout is 45 because he has a large DKP lead.  Casie's DKP is higher than, but close to Doogie's, so her cost would be 63 if Sakura passes.  Whether it's worth the over double DKP cost absolutely depends on the item and what's left for the potential spender to upgrade, and/or how much they want to just leave to luck next time.
Loot Council Rules
Minor Upgrade / Sidegrade Freeroll - If the item in question is one in which all rolling consider a minor upgrade or sidegrade, and the officers agree, the item goes to the top roller for minimal DKP charge.  The buyout option doesn't apply here.
Normal DKP Rules - Everyone is eligible to win the item, and DKP rules are as described above.  
Minor Loot Council - In comparison to others bidding on the item in question: players performing notably below average, who are new to the guild, have gotten too many items recently and/or have terrible attendance are voted to be excluded from consideration for receiving the item by the officers.  In the cases where one person is a poor performer and the other's attendence is low, some officers may vote to allow each to roll-- this will be a case by case analysis.  It takes a minimum of 3 officer votes (occuring in officer chat after rolls are made) to enforce this as to lessen the subjectness of one person making the decision.  DKP rules then come into play for those left over to decide who receives the item.
Major Loot Council - Players who are performing well and have high attendance will be considered first for any items categorized like this.  The same procedure will apply here as with the Minor Loot Council category, but it will be significantly more stringent and the officers will eliminate people more liberally.
Full Loot Council - Each officer will vote for a single person to receive the item in question based on overall performance, attendence, etc by whispering the most senior officer in raid.  If there is a tie, normal DKP rules will again apply to those chosen.
Item Costs and Applicable Loot Rules (ICC)
Item Type Base Cost Loot Rule
Minor Upgrades (as decided by Officers) 3-6 Minor Upgrade / Sidegrade Freeroll
Helms, ilvl 264 6 Normal DKP Rules
Shoulders, ilvl 264 6 Normal DKP Rules
Chestpieces, ilvl 264 6 Normal DKP Rules
Gloves, ilvl 264 6 Normal DKP Rules
Legs, ilvl 264 6 Normal DKP Rules
     
Tier Tokens 15 Minor Loot Council
Rings, non-BiS 15 Minor Loot Council
Neck Items, non-BiS 15 Minor Loot Council
Bracers, non-BiS 15 Minor Loot Council
Trinkets, non-BiS 15 Minor Loot Council
Belts, non-BiS 15 Minor Loot Council
Boots, non-BiS 15 Minor Loot Council
1 Handed Weapons, non-BiS 15 Minor Loot Council
Offhands, Shields, Stat Sticks, non-BiS 15 Minor Loot Council
Hunter Bows, 2 Handed Weapons, non-BiS 23 Minor Loot Council
     
Rings, BiS 30 Major Loot Council
Neck Items, BiS 30 Major Loot Council
Bracers, BiS 30 Major Loot Council
Belts, BiS 30 Major Loot Council
Boots, BiS 30 Major Loot Council
Offhands, Shields, Stat Sticks, BiS 30 Major Loot Council
     
Saronite Ores 2 Major Loot Council
Shadowmourne Quest Blood 15 Major Loot Council
Shards from the Throne 2 Full Loot Council
     
Trinkets, BiS 30-60 Full Loot Council
1 Handed Weapon, BiS 30-45 Full Loot Council
Hunter Bows, 2 Handed Weapons, BiS 45-60 Full Loot Council
Items w/ click-use or other major special effects 30-60 Full Loot Council