The RDM Maat battle isn't as hard as everyone makes it out to be. I realize that this post would actually be better in the Red Mage forums, but I may as well put in my 2 cents here :)
The key to winning is controlling the fight; this should come naturally to any RDM who solos on a regular basis. Your best friend in this fight will probably be the spell Aero III. None of your other spells will be strong enough to do much damage...and I'm assuming you don't want to melee him to death?
Start the battle BEFORE the battle by buying medicines--they will ensure your success. Some people complain that they are too costly, but you don't NEED vile elixers or vile elixer+1 to win. Heck, super ethers are only 30k at the moment and they give back 100mp per use.
If you REALLY want to go overboard, get a couple hundred exp tnl and bring an exp scroll with you. Often called the "cheater's method," it is an intuitive way to get full hp and mp instantly during the fight. It's not necessary, but it helps. And if Maat is beating the crap out of you, it's a good way to instantly get full hp and mp.
The next part people debate on all the time. Go in without armor? Buff first? Dispel first? Sleep first? Which buffs should be used? Which debuffs should be used? What day should you go in
From my own personal experience with Maat, I simply went in with full gear and slept him. Darksday is good for sleep bonus, Windsday is good for Air bonus, but really, any day but lightsday should work well.
After I entered, I buffed my character full with protect/shell/stoneskin/phalanx/blink. After that, I took turns dispelling him, then using some potions to regain mp inbetween casting times. Paralyze is good to use, but don't silence or dia him.
Eventually, Maat woke up. However--thanks to blink, stoneskin, and phalanx, I was able to land another sleep 2. This gave me enough time to finish bringing my mp back up to full. And thus, the carnage ensued.
From here on out, alternate Aero III and Sleep/Sleep II. Watch out for two things: your timers, and your buffs. By watching your timers, I mean don't cast Aero III until your Sleep 2 spell is ready; if you do it too soon, you may soon be kissing dirt. Keeping blink/phalanx/stoneskin up at all times will decrease the likelyhood that you will be interrupted while trying to sleep Maat.
Once your MP starts hitting to ~30%, consider using your convert macro. If you haven't used that scroll by now, do it instead and save yourself the time. Also, make certain that blink/stoneskin/phalanx are up. Chainspell + Aero 3 Maat to death, and you're done. In fact, you don't even have to get him all the way to 0...just to about ~25% health.
Oh...and learn from the mistakes of others. In my case, I'd say to take out any and all /wait from your macros. The problem on my first real fight was that I had a /wait 1 in my Aero III macro. I copied my macro from my EXP magic burst...which incidentally had a /wait 1 in the middle. Chainspell doesn't like to wait.
At that, you're done! So in the end: come prepared, don't be stingy on the meds, and don't freak out. As long as you can control the battle (and have the meds to keep you alive), you are guaranteed a win.