I made a viewfinder by using components from a disposable camera, CD-ROM driver and some LEGO bricks. Here is the result:

The viewfinder body is composed by three parts:

Here is the view of the assembled viewfinder parts. I only use Scotch tape, rather than glue, on both sides of LEGO to attach the top and bottom parts, in case I need to disassemble the viewfinder to clean or replace the lenses in the future.

Here are the parts for the base. The bolt and gear (dial-wheel) came from an old CD-ROM driver.

The clear plastic parts are cut from the clear plastic cover of a CD-ROM or DVD holder. I also use the same plastic on my Xbox VGA converter project years ago, like this:

The constructed custom hot shoe base for Sony NEX 3/5 series looks like below. I drilled a small hole on the top of LEGO, so that if the dial-wheel failed, I can use a screwdriver to attach or detach the custom hot shoe base.

Here is how it looks when attached to the NEX-5 body:

This is the front view of the LEGO viewfinder and the base part:

You can put any extra LEGO part above the viewfinder, if you really want to do so

Of course, I don’t really put anything on top of the viewfinder.