Make a Gryffindor scarf by crocheting, knitting or felting. Note that the knit scarf pattern has thick blocks of color instead of the thin lines of the Gryffindor scarf that the older students wear.
Start out with a gold tie (compare prices). Use red fabric paint to add the lines on the tie. If you're using paint and a brush, employ a ruler to help you make straight lines. A fabric pen works much easier in this case and most fabric stores have them in many colors.
Make two thick lines, then skip an inch and make a very thin line. Skip another inch and repeat this pattern.
The Gryffindor Robes
Make your own Gryffindor Robe in any size. I takes just minutes with this easy tutorial:
Ron has red hair, which is easy for most hair color types to dye. If you have especially dark brown or black hair, this can be a little difficult. You can try the spary-in hair color, but be forewarned that it will rub off easily onto your clothes.
Carry around a broken stick or a stick that has been broken and obviously taped back together. A busted wand is a sure sign that you're playing Ron Weasley.
Any thin stick can be made into a wand. Peel off any bark and use a piece of sandpaper to smooth down the sides of the stick. For a pointed end, use a small knife to whittle the end of the stick. Shaving the end of the stick should be done with adult supervision. Apply a dark or light wood varnish to your smoothed wand.
I suggest looking in a few local thrift shops for these simple elements. Find a white button-down shirt and a black or gray vest to wear over it. Wear a pair of black slacks, or make your own simple black drawstring pants. Black dress shoes will work for your feet. If you're going to be a more casual Ron, try to find a large red sweater and khaki pants. Dirty sneakers will work for casual Ron.