A few ways comes to mind.
1. Go to a 3D view, then in properties, turn on the section box. You can then select the box and cut away the view. The only issue is it must stay as a box. So you can't do a wierd angle.
2. In the project browser, select the 3D view. Right click and make a duplicate. Now, open the duplicate and turn off all the things you don't want. For example, I do this and only turn on my steel framing. That way I can easily see my framing in 3D when I'm designing it. I rename this view framing and it's always there, ready for me to use without having to mess with the original 3D view.
3. Set up a camera and pretty much do the same thing.

Now I like these kind of postings... Simple question, with an example. :thumbsup:

There's a few things you can do here:

1. Use a scope box. Open a new 3D View, orient it as you like and in the View Properties turn on the Scope Box. This is like a 3D Crop boundary that let's you crop the 3D view to the extents you'd like
2. Open a new 3D View and hide all elements you don't want to see. This gives you somewhat more control of which elements you want to hide but can be a lot of work in big projects.

Anyway, when done, freeze the view and you can tag and dimension the 3D elements...