Here is the basic template. It's purpose is to try and consolidate work and limit repetitive rules writing.
WS-7; BS- 6; S- 5; T-5; W- 4; I- 7; A- 4; Ld- 10
Son of the Emperor: A Primarch has the Eternal Warrior, Feel No Pain, and Fleet special rules. He is also immune to all psychic powers without a given Strength value.
Father of the Legion: If a Primarch with this rule also has the And They Shall Know No Fear special rule, the Primarch may choose to automatically pass or fail any Morale check he is called upon to take, and confers this ability to any unit he is with.
If a Primarch with this rule also has the Fearless special rule, the Primarch confers the Fearless special rule to any unit he is with.
Eversor Lamina: This is a master-crafted power weapon that can be used one-handed or two-handed.
If one-handed, the Primarch counts as striking with +2 Attacks.
If two-handed, the Primarch counts as striking with +2 Strength and adds an additional D6 to armor penetration rolls made with the weapon, but cannot claim the Attack bonus for wielding multiple close combat weapons.
Aegis Imperator: This is a suit of artificer armor that confers a 5+ invulnerable save and a Teleport Homer. In addition, the Primarch may teleport onto the battlefield exactly as if he were equipped with Terminator Armor.
What do you think?