Since I want to run as much of the LED Christmas Light wiring internally to keep the wires hidden, I'll be up in the attic and moving back and forth quite a bit. Even if the LED project doesn't work for some reason, I plan on living in this house for a long time yet, so an attic catwalk would make things a lot more convenient.
My access to the attic is from the outside of the house, through a hinged vent. Other than the ladder climb, it's a lot easier than popping through a hole in a closet ceiling somewhere.
Just inside the hatch I built a small platform about 2 feet by 4 feet so I wouldn't have to go into a balancing act the moment I got into the attic. As part of the house construction, they ran a 2x4 down the hole length of the attic as bracing for the trusses. In the picture below, you can see how I had simply laid down pieces of OSB (you could also use plywood, but I had OSB) across the trusses with the 2x4 holding them in place along the bottom edge. This worked for the short time I needed to be up there to install the homemade digital antenna you see in the photo, and to run the wires from it into the house. However, the angle makes it very awkward to maneuver and greatly increases the chances of tools and supplies falling into the blown-in insulation.
The first step was to make some brackets that matched the angle of the attic truss and act as a support for the actual catwalk. Rather than buy new lumber, I decided to use up as much of the wood I already had sitting in the garage. Two birds with one stone -- an attic catwalk and a cleaner garage. I ripped a few 2x4's in half, lengthwise, added the angled cuts, and then cut some more scrap OSB into braces. To assemble the brackets, I used construction adhesive (I think PL-400) and a finish nailer to hold the pieces in place until the adhesive cured. Then I widened the top of the brackets with a strip of OSB to make it easier to screw the catwalk planks to them later.
Here's what it looked like with the first brackets in place. To install them, I used construction adhesive wherever the bracket contacted the truss...
...then two screws through the OSB brace into the truss and, at the last minute, decided to add another screw through the top end of the bracket (the top right of the bracket in these pictures) into the truss. This last screw was mostly to keep the top of the bracket lined up with the truss while the adhesive cured.
I decided to mount them close to the insulation and lower the previous access I had to give myself a little more headroom. I used the previous platform as a work space to install all the brackets along the length of the attic.
For the "planks" to create the attic catwalk's horizontal surface I again turned to what I already had in the garage. I ripped a full sheet of OSB into three 8-foot lengths, and then a couple of shorter pieces to create another 8 feet's worth. That gave me 32-feet of catwalk, plus the 2 feet already provided by the platform inside the attic hatch. The 34 feet easily gets me to where I need to try and access the gable over the living room for the LED Christmas light project (though not quite to the far end of the attic).
To add some stiffness to the OSB planks, I glued (construction adhesive) and screwed rails along each edge. This also helps keep tools and supplies on the catwalk while maneuvering through the attic. The rails are about an inch by an inch-and-a-half and made from scrap I had lying around.
Mounting the catwalk planks was as simple as setting them in place on the brackets and screwing them down. This is the one place I didn't use adhesive just in case -- for some unknown and unforeseen reason -- I need to remove them for access.
The finished project is way more solid that I had anticipated, with no flexing while moving around on it.