Here’s a list of Perks to select from levels 21 to 30 with the Best Power Armor Build Guide in Fallout 4:
Level 21 – Armorer 2
Level 22 – Science! 2
Level 23 – Heavy Gunner 3
Level 24 – Scrapper 2
Level 25 – Gun Nut 2
Level 26 – Nuclear Physicist 3
Level 27 – Armorer 3
Level 28 – Science! 3
Level 29 – Scrounger 3
Level 30 – Demolition Expert 2