Here at HO Scale Customs, when we build a structure or any detail on our layout, we do so to grab the viewers attention and make them say “Oh! Wow! Check it out!”, “Look at what they did there!” To us, the ultimate rush in the hobby is the reaction to the details that create reality. Remember we the modelers are also the viewer! You want to look at your project and think, “Yeah, I did that!” After all, this hobby is mainly for you!
One of the first places on a structure that the eyes draw to is the roof. The eyes draw down after that to the rest. Everything else is under it! And if you have an eye-catching roof with realistic detail, you will start the vision of your art with a positive impression.
A lot of our structures and roofs, we admit it, are bitched up. Ripped tar paper, lots of repair or repairs needed, dirty, grimy, stained and looking like they have seen some life. The best part is? It is so easy to do! You obviously don’t want to make every roof in your town look worn, but just laying paper, all neat and pristine will look ridiculous too. At the very minimum, add some chalk pastel dusting, a turned up shingle, … something! But making a roof appear beat can be a lot of fun and something you should never fear!
TAR-PAPER LIKE “JOE THE ROOFER”
Get out your knee-pads, grab your hammer (figuratively), and roll up those sleeves! You can make your tar-paper of a number of different materials. Some of the most common are colored construction paper in blacks, grays, dark red, etc. Or copy paper painted with acrylic paints of the same shades which gives it a nice crisp touch to it. Just make sure to paint both sides of the paper. 
Whatever you choose, cut it into strips when its colored (if painted). Make the strips about 12 scale ft. in length. Start from the bottom edge with about a 1/16 inch overhang, left to right. butt the side edges of each strip up against each other and overhang on the sides a tad. Some of your lengths will obviously be shorter at the sides. Which is good we want seams to be various and not line up. when you begin the next row overlap it about 1/16″ to 1/8″. until you get to the peak or the other end (on a flat roof). If it is a peak put a thinner strip that straddles the peak end to end to cap the roof. You now have what should be a freshly laid roof. But you want a badass roof right?
EVERY LAYER TELLS A STORY
When you weather something in this hobby, think about it as layers. That first layer is ok, but every additional layer brings more and more depth to your work. Sure you have tar-paper. Plain one color one-dimensional tar paper. But beyond that is the fun adventure! So let’s start building and beating this roof up like mother nature intended.
We like to begin by taking a synthetic sponge, dab it in some light/dove gray or off-white colored acrylic craft paint. Then press that sponge (Or better yet a craft sponge on a stick, round is our favorite) to some newspaper or paper towel and get as much paint off of it as possible. Sort of like you do when you dry-brush. Then very gently dab it onto your darker roof, trying to get micro-tiny little dots on top, but so faint that it just lightens it all out. Don’t panic if it is a bit heavier on the very edge, it will look cool when it dries. Don’t go crazy here. When done and it dries it should give the appearance that the sun bleached out the roof. Don’t freak if you got a few dots a tad bigger. Remember, Birds poop on roofs. And if you think you went to heavy in areas, just repeat the process with black or dark gray to where you want.
BEAT THAT ROOF LIKE IT OWES YOU MONEY
Let’s start with that overhang on the edges of the structure. Trim some to the very edge. Leave sections hang out, snip, tare, hell, bite it off and make it look a bit ragged if you like. In time all edges start getting chewed up. 
Now let’s get a little crazy here. Where the paper overlaps each layer we are going to scrunch up some of that in various random areas on the roof. Take a blunt flat object like a popsicle stick or even better an emory board because it may scratch some junk up!! You can use the back rounded end of a pair of tweezers, etc. Now go to that flap overhang and with a slight downward push (don’t cave in your freakin roof Hercules!) push it upward about 1/16 to 1/8 inches. Yeah, yeah, yeah you might tear it a little, but you are pushing it away from the lower row. You will also probably expose some of your actual 
cardstock or styrene roof. Expect that and forget that for now. Whatever. You got more roof to booger up. Don’t do this everywhere and make it look like a tornado passed through. Just a few random spots across the roof here and there.
Get your hobby knife, Dr. Frankenstein! No, we are not using the razor’s edge, but the dull backside of the blade, so watch your fingers please! and we are going to gently drag it downward at the very edges of the overlap you didn’t jack up with your stick. Don’t do all the edges. Again, randomize it. You are basically just scratching at the edges maybe 1/32 to 1/16. tugging and ripping at it so it frays. Don’t worry if you pull away some fuzz of the paper. When satisfied, moderation on all of this is wise, take a break and look at it from all angles. Make sure it is like you want it.
You can put a few tiny holes here or there (in the paper only!) with the side of the knife if you wish. Old roofs leak. It has to leak from somewhere. Now lastly, using the color you painted the tar-paper, dab it on over the areas you exposed cardboard or styrene, and along any white paper edges the tearing often produces. This will give it a natural matching look.
At some point in time in a roof looking this old, somewhere, someone, would likely have put on some tar patch to fix one of them leaky seams. We make tar patch by mixing a small amount of white glue with black acrylic craft paint. Don’t use gloss, the glue will give it enough sheen, and we are just going to dull some of that sheen down later, so don’t think you ruined it with shine either. You can’t possibly ruin this roof at this point anyhow, right? Take a toothpick and use it to paint short, thin, random lines at the seems and joints. Again don’t overdo this. If the guy took care of his roof to begin with it wouldn’t have deteriorated this far, so we doubt he did too much patchwork.
DUST, DIRT AND OTHER FUN ELEMENTS WE OFTEN NEGLECT
Using ground pastel chalk/pigments we will put on a layer of soot, dust, and dirt. We start with black. Using a flat brush pick up a little from your container and tap the brush to sprinkle a little here and there randomly across the roof. A little goes a long way, so start light. Then simply swirl it around in areas to darken it out with soot. If you have a chimney or smokestacks added to the roof, go heavier around them. If not, in a town you likely still would have soot over many years from nearby buildings. The stuff kind of travels in the air yanno?
Make sure to dust over your tar patch too. It will dull the shine and make it look older.
Now repeat the process with a very light brown to give it a dirty dusty look on top of black. again, go lighter to start. This will give another layer. You don’t want to overdo this, but the brown will give those torn edges a lighter look where some dirt has built up.
Add white ground pastels along the edges of each row of tar paper in an extremely thin line enough to highlight some more sun fading. and then add a medium gray to diffuse any too white sections.
With all the dust done, lightly blow (yes with your lips and not an air can) any excess powder. We never spray any clear or dullcoat on our models. then repeat with any shade where you don’t feel satisfied. You can also add outbuildings, elevator shafts, billboards, extra smokestacks, air conditioners, and even some old scrap wood planks to the top. Paint some rust streaks down from a metal stovepipe or smokestack with some thinned out burn sienna, terra cotta, or raw sienna. Make your roof scream out for attention!
Now stand back and look at your handiwork! You have created detail in layers and I am guessing it looked pretty darn sweet! All of this, like anything, just takes practice, but the less you fear experimenting with different mediums and products, the more experienced and creative you will become as a modeler!
