Late Summer Internship: Sample Model Needed

Hello,

I've been reaching out to a bunch of boutique firms via email/LinkedIn. I just got an email from a member of the firm who said they do not typically take on interns because they are small, and do not want to use resources for training, which I understand. However, he mentioned that if I send him a sample model showing my skill we can talk which may lead to an internship. Anybody ever done this, or had this experience. I'm not sure how to go about this or how in depth to make it.

Any advice would be greatly appreciated.

Thanks in advance.