1) Go to Admin > Design > Layouts and create a new layout.

http://i.imgur.com/F32Ggr5.png

2) In layout settings use product/product as a route.

http://i.imgur.com/W6VFtBl.png

3) Set a design override for the product(s) that you want to have different layout.

http://i.imgur.com/SKOjZXt.png

4) Go to Page Builder > Content > Layout: YOUR NEW LAYOUT and create your custom product page.