If you are dealing with print publishing, or graphic design that would be used for publications, the correct terminology would be that you are "setting up the layout" or "designing the layout" of a particular item, with the latter be the predominant structuring.
If you are dealing specifically with web design, you could use the above (with the preference being "designing the layout"), or, more specifically, you could say you are "creating wireframes."
If you are dealing with type and fonts, you would be "setting the type" or "typesetting."
All of these things could be done within the same project, just with different media or on different parts of the same medium/media.
For a more extensive list of terminology used in page layout and design, you can go to About.com's Desktop Publishing portion and peruse their glossaries.