So, here is what you will need.
For the blouse:
Light weight cotton material
Matching or contrasting thread
A strip of fabric (or ribbon) at least a metre and a half long
Tailor's chalk/vanishing pen
For the pattern:
Large pieces of paper/light card (the weight of the paper isn't important but it will be easier if it is plain)
Ruler and tape measure
Masking tape or sticky tape
Measure from shoulder to shoulder, then from your collar bone to where you would like the bottom hem to sit. Divide the first measurement in half and add an inch and a half (4 cm) seam allowance. Add a three inch (71/2 cm) seam allowance to the length.
Now measure the circumference of your arm at the widest point, then measure down your arm to where you want the sleeve to stop. As the sleeve will be double the arm circumference, we only need to add five eighths of an inch (2 cm) seam allowance to the length.
We're going to take those measurements to make two rectangles that should end up looking like the ones in the pic.
Stick these pieces together in position and pace another piece of paper underneath at the top of the blouse 'pattern' - this piece needs to be large enough to 'cover' the gap between the arm and the bodice. Stick the pattern to this extra piece.
Create a gentle curve underneath the straight line. This is going to form the neckline so try not to make the curve too deep. Cut away the excess and you have your completed pattern!
It's easy peasy from here on in....
Place the right sides together and sew the side and shoulder seams. Press all seams open.
Mark how deep you want the drawstring channel to be with chalk or an air vanishing pen. If you're using a strip of material for your drawstring, make the line at least two inches (5 cm) long.
Cut down to the bottom of your mark and sew down the raw edges.
Now, we will need to press down a small hem about a quarter of an inch (1/2 cm): but we will not be sewing this...
Here's the dull bit! Double hem all of the remaining raw edges.
If you are using a fabric strip, take note thins is a long process!
Take your (very) long strip of fabric and press a crisp line down the centre. Open the fabric back up and fold each raw edge towards the line you just pressed and press again (don't be tempted to cut corners at this point as you'll only have to re-press later) Now fold the fabric along the centre line and (yep, you guessed it) press again.
Tuck the ends under and sew a straight stitch along the open side.
Your blouse is now ready to wear!
(N.B This blouse can be worn both on and off the shoulder, but if you're going for 'on' try and choose a fabric less busy than mine!)