* Hay un desfile de moda en mi habitación: This is the most literal translation and works well if it's a formal or planned fashion show.
* Estoy haciendo un desfile de moda en mi habitación: This translates to "I'm doing a fashion show in my room" and is better if you're the one putting on the show.
* Se está celebrando un desfile de moda en mi habitación: This translates to "A fashion show is being held in my room" and is more formal and less personal.
* Tengo un desfile de moda en mi habitación (informal): This translates to "I have a fashion show in my room" and is a more informal way of saying it.
The best option depends on who you're talking to and the overall tone of the conversation.