Help me graffiti my own garage

What's the wall made of? What's the condition of the surface? You may want to start with a solid paint marker, also known as a "streaker". They provide excellent coverage on most surfaces and won't drip, so you can take your time creating your design. Very user friendly with great waterproof qualities. You'll get a nice, opaque black that is unmatched in the field of non-drippy markers. The http://artprimo.com/catalog/sakura-solid-markers-p-672.html is the classic streaker. Time-tested, graffiti artist approved. There are http://artprimo.com/catalog/art-primo-solid-paint-marker-p-3326.html, which may be a better value, but I don't have personal experience with these. It is a bit unorthodox to use streakers for large pieces and, depending on the scale of your design, you may need several markers to complete the project. But given your requirements and abilities I think it could be a fine solution. They'd work well for guests signing their names as well.

We ended up using Sharpie paint markers, which are easy to get and we can have several of them on hand. People love signing our garage, especially little kids, who are like, "WE GET TO WRITE ON A WALL?" The peeling paint now looks cool. It's become a showpiece where people like to linger and read all the names instead of an ugly-ass wall that I hate, and when it dominates the view and we find ourselves staring at it, we love it because we get to see the names of all the people we love. A+++ would graffiti again.

I'd go with regular old-fashioned spray paint. Use a stencil to make the quote look a little neater.

For the main quote, I would outline the whole thing with pencil (using an overhead projector if you can get your hands on one), then trace over that with paint pen, then fill in with traditional brushed-on paint (latex exterior paint, I'm guessing, but talk to the hardware store). Folks can sign in paint pen. Sharpies will also do in a pinch. I personally think it would be kind of cool to either outline the text in silver paint pen/sharpie or offer guests that as an option to sign, just to add a little visual interest to the whole thing.

Art supply stores (read: not Michael's) have huge Sharpies including the ones with oil-based paint. They'll also have pro-level spray paint and stencils and stuff.

I'm just going to freehand the quote; I'm very comfortable with that part. I'm not going to stencil. I'm looking for help on what type of paint/marker/whatever to use for doing this kind of thing outdoors, not on how to design it.

Oh, then yeah, paint pens, and maybe some brushes with regular outdoor paint if you plan to make the text too thick to fill in with paint pen easily.

Go to the hardware or office supply store, there are http://www.staples.com/Sharpie-Magnum-Chisel-Tip-Permanent-Marker-Black/product_272716 chisel-tip http://lofgreens.com/avery/avery-marks-a-lot-jumbo-chisel-tip-permanent-marker/AVE24148/p. I have always liked marks-a-lot markers; lots of ink and pretty permanent. also, pictures of completed project, plz! also, perhaps people could draw a plant along w/ signature - anybody can draw a flower. Those streakers look good, too, though. If you use markers, you could spray polyurethane on it to stabilize it a bit.

My experience with the commonly-found http://www.michaels.com/Sharpie-Oil-Based-Paint-Pen/gc1650,default,pd.html has been pretty "meh", especially after it's been sitting unused for a while. It takes a pretty fair amount of shaking and pressing and shaking and pressing & repeat repeat repeat to get the paint to flow properly. So I'd recommend not bothering with those, FWIW. http://www.sharpie.com/enUS/Pages/fine-point-marker.aspx tend to not do so great on rough or wet/damp surfaces, but they're available everywhere and cheap (especially if you buy larger packages online), so maybe worth giving one a try. The ink cleans off the skin easily with rubbing alcohol or just some mildly rigorous scrubbing with ordinary soap and water. (I just tested this on my finger to make sure.) I can't honestly say how tough it is to get the marker out of clothing, because I usually use black Sharpies while wearing black t-shirts & jeans/shorts that don't need to be pristine, so I don't care if I get a few marks on them. Since it seems likely that young 'uns will be using them, you might want to do a laundry test or two. (Note: I'm thinking more about what your guests will use to sign the wall, less about what to use for the main quote.)