I had a limited amount of money and time so I had to improvise with some of the costume, it could probably be made easier if you have access to a red and white striped jumper or a yellow boiler-suit already, but I didn't, so this is how I did it.
Step 1: Materials
For the main body:
Plain white collared shirt
100% cotton pure white boiler-suit
Golden Yellow Rit dye powder (two 31.9g boxes)
One red zip the length of the boiler-suit body
Two red zips for the pockets
One red felt square large enough to cover the back of the boilersuit
Two small felt squares to create the 'm' logo - one red one yellow.
For the legs and arms:
Red and white thigh high stockings (two pairs)
Old pair of shoes and red paint
Yellow shoe laces
Yellow marigolds / rubber gloves
For the face:
Red clown wig
Black and red makeup
Step 2: The Body
Next I heated enough hot water in a metal bucket (saucepans were too small) to allow the cut down boiler-suit to move freely and added the dye, stirring it to mix the dye properly. I then added the boiler-suit to the dye bath, stirring the boiler-suit for 20 minutes until the yellow had been absorbed into the cotton.
Once the dye had been absorbed I rinsed the boiler-suit in warm then cooler water until the water ran clear before hand washing it in detergent and hanging it to dry.
Rubber gloves were essential for dyeing as the water was hot, I also didn't want yellow hands... I made sure to clean everything I used for dyeing as soon as possible afterwards too. Obviously if you can find a yellow boiler-suit you'd be able to avoid dyeing anything!
After the boiler-suit was dry (which took around a day) I turned the legs and arms inside out, folded the fabric and sewed them to make a hem.
For the white collar I simply turned the boiler suit collar inside out and wore the collar of my white shirt over the top of the boiler-suit.
Step 3: The Arms and Legs
As my white shirt had full length sleeves the first job was to cut these sleeves almost completely off, I left an inch or two on the end. Then all I had to do was simply put a hole in the foot end of one of the pairs of socks, pull them up and safety pin them to the shirt.
Step 4: The Shoes
When the shoes had dried I used yellow laces to finish
Step 5: The Details
The boiler suit fortunately came together with poppers instead of buttons or a zip, this made things easier as it enabled me to cheat and so I glued the large zip over the top of the poppers, meaning I could still use the poppers to fasten the boiler-suit. I attached the small zips in the same way.
Next came the logos. I used felt for both the front and back logos as it doesn't fray. With the front logo I cut a red circle and stuck it over the pocket, then cut an 'm', glueing it on the red circle. In hindsight it could have been easier to just cut the 'm' out of the red circle as the boiler-suit was already yellow...
For the large 'm' on the back I cut it out like before, I decided it would be best to glue it on when I was in the costume as the boiler-suit was quite elastic.
Step 6: The Face
So I started with a layer of liquid latex (with a lot of help from my friends Olly and Tom as my hand eye coordination is terrible, especially backwards...), waiting for it to dry before applying a little toilet paper in the places where I wanted wounds. I then applied a second layer of liquid latex.
Once that was dry the toilet paper was ripped apart and the insides filled with black then red make-up. After that my face and neck were plastered in white face paint. Once that too was dry I used some red face paint for the nose and lips to complete the clown image, for the hair I had a generic red clown wig.