Here is an alternate Undead build path, one that boasts impressive mid-game oppression that can net the player Maidens at 30 minutes. It is not without it's flaws, but for how simple it is, it is surprising how strong and survivable this build can be.

1. Purchase Skeleton Archers. Research Attack to 4. Tempo loss: nonexistent. Tempo gain: very high.

This initial step of the Skeleton Archer purchase is still a necessary staple of your start out, even though the whole build is not quite optimized for it. Skeleton Archers still serve as that highly important and valuable damage dealing in the beginning.

2. Purchase Necromancers. Research Necromancer Trainings 1 and 2, Research Meditation 1x. Tempo loss: High. Tempo Gain: Very High.

For once we may finally say Necromancers have decent use in the Undead army. With the ability to now cast AOE Unholy Frenzy on Skeleton Archers (and Orcs as well), they provide valuable support for your damage output. The initial purchases expand the Necromancer mana pool to make decent use of their spells. Raise Skeleton Warriors provide good early bulk that isnt the easiest to dispose of.

3. Purchase Skeletal Orcs. Tempo loss: low. Tempo Gain: Moderate.

This purchase is to simply add some bulk and optimization with your necromancers. Their bounty is only around 30 gold and the spawn rate is decent.

4. Purchase Heroes.
My personal preferences are Death Knight + DreadLord, but Unholy Aura is a must.
I like Vampiric Aura because it stacks with Undead lifesteal and can add good bulk to your many melee warriors. The Double Nukes are also a good additional way of netting additional gold.

5. Finish Upgrades. All Meditation Upgrades. Melee Armor, Melee Attack to 6. Lifesteal. Ghoul Frenzy. Ghoul Upgrade. Skeletal Longevity. NOT RAISE SKELETAL MAGE.

All these purchases are to simply flesh out the overall potency of your army.

6. Purchase Maidens.
This build is quite reliable in survivability and killing power to net you Maidens and it doesnt boast a unit over 2000 gold, which is quite impressive. The Maidens will be the main damage dealer in your force and provide you a foothold and win condition.

Notes:
This army is lacking on any anti-magic capabilities. You have nothing to dispel the enemy with. This army is not dependent on healing or unit preservation. Necromancers with Meditation have good Hp and decent damage as well as Skeleton Archers. Your Melee units have fast spawn rates and Skeletons are continuously summoned en masse.

This build is incredibly potent against Alliance if they do not purchase Priests to dispel your army. It even does all right even if they do have priests as your necromancers will have better mana sustain than priests. However expect to gain no ground if assaulting the enemy at their base as priests will enjoy infinite mana. You only need a single necromancer with a lot of mana to buff all your skeletons. If you select all your necromancers and cast unholy frenzy once they will all cast it and mana is wasted.

You will flesh out your army after the Maiden purchase. You will get Aboms, Gargs, Wyrms, etc. However: you will eventually lose micro on your necromancers and you might not even have destroyers. As a result, the full Undead Army is still WEAKER than all the other armies. But, the early Maiden purchase and a full stack of Maidens ensures your high Gain and still provides you a win condition. If you are able to get Nagas Secret first, it will greatly strengthen your army.

Without Trueshot Aura, your Maidens dont have much in the way of boosted damage. Their potency isnt as high compared to the other Undead build.