Printing Different Sized PDF

I would like to know the best way to set up my designs for print by others.

I will be sending my clients PDF's of designs I have created specifically for them. They will either print them on their own or bring to print center, most likely Staples type.

1. I need to send in PDF


2. Clients needs to be able to choose size - especially poster size.


3. Prints need to look good

I have created a design in Photoshop & saved it as a PDF, however when I try to print it as Poster I am only seeing an 11x14 size??

Thanks any help is much appreciated!