He's pretty big...measuring about 41 inches wide by 61 inches (104 x 155cm) tall...
Here he is with my son who will be three this weekend, to give an idea of scale..
I created him over at Spoonflower to match the rest of the room, that you can see in these posts:
Spoonflower have a maximum decal size of 30 x 30 inches. Don't let that stop you from creating something big and bold though! You just need to put careful thought into where your joins might be.
Mr Mikey Robot is actually 9 different pieces...all carefully cut out by me from two 30x30 inch decals.
I took the robot I had drawn, enlarged it to the finished size I wanted it, then broke it into logical parts, juggling it around to make it fit the two decals.
Once it arrived, I cut out the pieces, then "tacked" them to the walls using spare offcuts of the decal background. Here are some shots I took after cutting it out, and while I was "assembling".
1. Choose a good contrasting background colour to give a good edge to cut around. Light grey on white might be a bit hard on your eyes!
2. Take your time re-composing your design. Tape it up on the wall before you peel the backs off to make sure you are happy with the placement.
3. Don't worry about keeping the orientation the same. Some of my pieces were landscape and some portrait - it really doesn't matter and you can't tell when it's on the wall.
4. Butt the cut edges together when applying to your wall - don't overlap them. If you overlap them, you can see the edge of the underneath decal through the top decal.
5. Don't be afraid to lift and move your decal. I pulled a couple of mine up more than once to get the joins looking perfect.
Result - one happy nearly 3 year old!