This is a fun project that anyone can do on a rainy day. You don't need much skill and is a perfect project for bored kids or, if you want to redecorate or may be need a back drop for a production, movie or play.
You will need,

A computer with an internet connection
A printer
Paper for the printer
Masking tape, blue and white.
Scissors
A straight edge and box cutter knife
A wall
About 2-3 minutes per page printed

Step 1: Designing Your Poster

We are going to be using free online software which is easy to use. go to http://rasterbator.net/
The software is very easy to use, follow along with the screen shots if you are unsure. The shadow person on the side gives you some idea of scale, and you are limited to 1000 sheet of paper unless you download the stand alone version.
When setting up the printer make sure you select the right paper size and tick the "fill entire paper" button
Once you have printed your poster its good idea to number them as its easy to get them out of sequence and can be confusing if you get a sheet in the wrong spot or upside down.

Step 2: Assembling Your Poster

Now for the fun part.
Most printers will leave a boarder on all four sides of the paper, but only two side need to be cut. This leaves a little bit of overlap and make the poster easier to assemble.

Good idea to number the sheets as the come out of the printer
So using the scissors or a straight edge and a box cutter, cut the right and lower boarders of each sheet.
Next using the blue masking tape carefully assemble the top row, and make sure its straight.
The row can then be flipped over and the back taped up with the white masking tape.
As blue masking tape is less stick it can be removed without damaging the print.
This can be repeat for the remaining rows
Once all the rows have been completed they can be joined together in much the same way, use the blue tape to get everything in position and then flip the poster over and use the white tape to give it strength.
Stick on your wall and freak out at you giant robot.....