Here is a list of herbs which make your chicken coop smell good and have medicinal uses as well. Mint, lavender, lemon, and rose petals can be used in nest boxes and coops to make your coops smell good but also work as a natural stimulant, is said to have a calming effect on your chickens, is a natural insecticide, deter rodents, and even have anti bacterial properties which slows the growth of fungus and bacteria which causes infections and multiple health problems for chickens.
Here is a partial list provided by Grit which have great potential health benefits for your chickens, as well as, make your chicken coop smell good
Smell good and are antibacterial
Basil - Antibacterial, also improves mucus membrane health
Thyme-Antibacterial
Smell great and act as an antioxidant, fungicide
Cilantro - antioxidant, fungicide, builds strong bones, high in Vitamin A for vision and Vitamin K for blood clotting
Dill - antioxidant, relaxant, respiratory health
Sage-antioxidant
Tarragon-pain reliever, helps sleep, smells like sweet grass
Spearmint-Makes nest boxes and coop smell minty fresh and can be used as an antiseptic
​Smell good Rodent repellents:

• Mint (all kinds) - insecticide and rodent repellent
• Lemon

Aids in the prevention of coccidia, salmonella, infectious bronchitis, avian flu, blackhead, and e-coli and makes coops smell like spaghetti...just kidding..

• Oregano - Sprinkle oregano in nests, bedding, and coop

Blood vessel development and keeps coops fresh and has a wonderful fresh scent for your nestboxes or coop

• Parsley - high in vitamins, aids in blood vessel development, laying stimulant

Helps nervous system, brain, and blood functions

• Pineapple Sage - aids nervous system, highly aromatic
• Spearmint
• Rose Petals - highly aromatic, high in Vitamin C

Pain Reliever

• Rosemary - pain relief, respiratory health, insecticide

Respiratory aid

• Thyme - respiratory health, antibacterial, antioxidant, anti-parasitic (1).

More About Herbs & Chicken Health

How to Keep Your Chickens Healthy Using Herbs

Garlic Herbal Treatments for Chickens

​How to Use Apple Cider Vinegar to Keep Your Chickens Healthy

​How to Use Probiotics to Improve Your Chickens Health

​Sick Chickens: Signs, Symptoms & Treatments

Fennel Seeds for Chicken Health

Wheatgrass for Chicken Health

References:

1. Lisa. (04/18/2012). Nesting box herbs-chicken aromatherapy. http://www.grit.com/animals/nesting-box-herbs-chicken-aromatherapy.aspx#axzz3OZu1MVYF