Create some cool plaid with the grid and the simple Transform effect. Use the Recolor artwork to get any color plaid you can imagine.
Create a grid under Preferences. Set the Gridline every: to 100 mm and set the Subdivisions to 10. Under the View Menu choose Snap to Grid and also choose Show Grid.
Each Gridline will be a darker gray, the subdivisions are a lighter gray. I refer to each darker gray sections as units. Draw a rectangle 9 units wide, 1 unit high. The rectangle will snap to the grid with the Snap to Grid turned on.
One the next set of units below, create one of color then one unit of black, repeat this for a total of 9 units.
Select the first tow rows created and duplicate it so there are 7 rows total.
Draw a 10 point line on the grid from corner to corner. Round cap the ends in the Stroke panel. Duplicate the line.
Select the line and choose Effects> Distort & Transform> Transform. Set the Horizontal offset to -10 mm. Set the number of copies to 100. Click OK. This will take the single line, duplicate it 100 times to the left, skipping every other sub-unit.
Move the Transformed set into position over the check board. This is an effect so the one line is simply transformed 100 times 10 mm each time. This makes it much easier to select one line instead of 100 if a change is needed.
To edit the Transform effect, open the Appearance panel and click on the Transform link.
With the duplicate line, choose Effects> Distort & Transform> Transform. Set the Vertical offset to -10 mm. Set the number of copies to 80. Click OK. This will take the single line, duplicate it 100 times skipping every sub-unit.
Move the vertical Transformed set into position over the checker board squares.
Duplicate the transformed lines, both vertical and horizontal covering all the black squares.
Create a smaller line the size of one subunit.
Turn off the Snap to Grid. Move the line so the center of the line is directly in the center of one unit.
Select the line and choose Effects> Distort & Transform> Transform. Set the Horizontal offset to -10 mm. Set the number of copies to 100. Click OK. Move the line into the vertical center of the first row.
Duplicate the row vertically 1 unit down. Set the first row of lines to white, the second row of lines to red.
Repeat the rows, white, red, white, red, white, red, white.
Repeat the transform with the vertical lines. Set the Vertical offset to -10 mm. Set the number of copies to 80. Click OK.
Select all the shapes and Group them. Object>Group.
Turn the Snap to Grid on under the View Menu. Draw a rectangle 9 units wide, 7 units high. Click on the Draw Inside mode at the bottom of the Tool Bar. Cut the Grouped art, paste it into the Rectangle. Click on the Draw Normal mode when done.
Nice Plaid, but how about some other colors?
Select the artwork and choose Edit>Recolor Artwork. Click on the Edit tab at the top of the Recolor Artwork panel. Click on the link icon to the lower right of the color wheel, linking the colors together.
Move the colors handles around he wheel to actively change all the colors in the plaid.
Try several different color renditions quickly with the Recolor artwork.