Roskilde hosts 1 festival in this guide: Roskilde Festival.
Roskilde has 1 festival in this guide. They run in June, and festival-day temperatures range from 21°C (70°F) to 21°C (70°F), with nights down to 12°C (54°F). That range is the reason there is no single "Roskilde festival outfit". The answer changes by month and by site.
1 carries a high rain risk, which makes waterproof footwear a requirement rather than a precaution.
The ground matters as much as the sky. Every festival here is on open field, which puts waterproof boots at the top of the list for most of these events. 1 of the 1 has camping on site, so outfits have to survive living in a bag on the ground for several days.
Stylistically the crowd here leans alt, camping, costume and punk. Roskilde Festival is the largest of them at around 130,000 people, and it sets the tone the smaller ones react to. None of that is a dress code. It is what you will see, which is worth knowing if you would rather blend in or deliberately not.
