Raid Mechanics
The attacker should not need a district to launch an attack from i suppose this is self explanatory but it needs said. Removing that gap gives everyone the opportunity to perform this action. CP cost should be proportional to actually sending an attack to take a district, for corps that own land, and be substantially less for corps that do not. This gives an endgame for corps that do not wish to participate in PC but rather be a pirate type corporation. This makes it more difficult for a corp in PC to try to manage raiding with the other CP actions. As much as i want this to be a big battle a raid, as opposed to a battle, is a small scale event and should be handled as such. 6v6 or 8v8 in a domination type match would be ideal for a raid.
Battles should also have no clone limit and play until the MCC is destroyed to allow sides to use as many resources as possible/wanted to achieve victory. A vehicle cap should also be in place of 1 major vehicle HAV/ADS and 1 minor Vehicle LAV/DS. This makes the match much more tactical and prevents a corporation from deploying 6 tanks to hold the one point.
A 1 minute warning should be all a corporation receives and this 1 minutes can be within 1 hour of your timer for example 0.H has a district timer set at 01:00 A raid can happen at 00:01-02:01 if the raid is placed at 00:00 or at 2:00. This is a perfect raid style timer. Making your opposition scramble to find people not currently deployed to defend against the raid. The War Barge should also only be 1 minute long. Many may disagree with this short of a warning but a raid should not give you advance warning because with greater then 2 minutes i can get the 6-8 of the best 0.H players into this battle as if we knew it was going to happen the whole time. Even with 2 minutes it will still be relatively easy to field a team to fight those battles.
I also believe multiple raids by different corporations on even the same district should be allowed. Doing so would cause those small elite corps like 0uter.Heaven the inability to field the players necessary to prevent all raids from being successful and keep us out of pubs where we destroy the hopes of many players. Since raids cost CP this makes corps that have districts less able to Send Attacks, Sell Clones, Move Clones, Change Timers and (if anyone read my previous thread) Change Map Layout.

Raid Benefits
Raids need to have great incentive for the competitive player base not currently in PC to use their CP to do raids. So in light of that statement i believe

A successful Raiding Corporation should receive PC style payouts (ISK and Salvage) AND massively increased chance for random officer gear drops. Should the match result in a no show by the defending corporation there needs to be a severe penalty either through isk or CP I currently don't know how to penalize and need help from the CPM's and CCP to make it worthwhile to at least provide a resistance or for the attackers to stay through a noshow. This further takes competitive players from public matches and gives the new players a chance to love the game.

A successful Raided Corporation will receive NO isk, Enemy Salvage and a Massively increased chance for random officer gear drops. The no isk part is essential as this makes the defending corporation want to be as efficient as possible. If say 0.H gets raided by P.E we will want to attempt to win the match with minimal casualties due to the isk inefficiency possibility. However if officer gear is more circulated we will finally see them used in PC due to the ability to have a reliable way to earn more.

I think allowing raids to happen 24 hours will quickly become frustrating for corporations being attacked by people on the other side of the world, and vice versa. It would lead to many attacks happening against corps that are likely asleep, and even if raid defense was open to alliance members, you would likely see massive holes in defendable time and a lot of boring no-show battles.

I think at the least allowing corporations to set a maximum 12 hour window where the district is vulnerable to being raided. It's large enough so that the window can't be hidden at an obnoxious time and allows for surprise attacks without a clear idea of when the attack will happen, but small enough that defenders can at least assure battles will happen on their side of the clock.

You're read this obviously but for those who have not:

https://forums.dust514.com/default.aspx?g=posts&t=187670&find=unread

Partially where I got the maximum 12 hour metric (even though I initially wrote it for Conquest battles and not Raids). I think allowing corporations to reduce the raid window a little is fine but it should probably still be quite a bit larger than an hour. Perhaps at max activity level Raid window can be brought down to 8-6 hours and Conquest down to 1.