When it comes to printing for your modeling portfolio, and headshot, consider:
8" x 10" is the size for a headshot.
When comes to prints of modeling photos for your portfolio the standard size is: 9" x 12."
Your portfolio should fit this size print. So a portfolio 12.5 x 9.5 would be best.
Your portfolio should be black or white- You can get one at B&H Photo or any professional photo store, could run from $40- over $100 dollars depending on the book. You should put only your BEST photos in the book. Don't try to rush and put every print in there, take your time. Your book represents you.
If you can not find a printing place in your town consider Adorama. Great prices. They print and ship nation wide.
I use them all the time for my modeling prints.