Hi Trev I would be happy to help guide you along the way of your project! I am in California. Are you in Australia? Is this going to be an electric board? - This might determine how much the board can flex and how the batteries will be mounted. Batteries don’t like to flex. Consult the pro’s such as onloop and torqueboards for that.
First things first. The most important thing in a project like this is having a complete vision of the finished item. You are really making a prototype board. Adding new ideas and features along the way may get you in trouble.
So the first step is to make a template. A full size cardboard cutout of shape of the board. That way you can stand on it on the floor and make sure it is the shape you want and that the batteries, motors, hardware will fit. It also helps give a vision of the finished product. Save the template! You will find yourself refer to it often. Once the overall length of the board is determined, cut the plastic to the that length. Do Not cut the final width yet!. (Save the scrap pieces for testing drilling techniques and drill bits. Some bits drill will leave a better finish others even though they look exactly the same).
Now make 2 pieces of wood or similar to place under the cut to length board. Place them where you want the trucks to mount simulating the wheelbase of the board. Then stand on the board and decide if the amount of flex is appropriate for your weight. Notice that adjusting the “wheelbase” changes the flex. If the board is too stiff, now is the time to think about making the board narrower and contour the front and rear to the shape and thinner to reduce the weight. Both the Width and Thickness will determine how much the board will flex. Adjust one at a time and sneak up on it slowly alternating small cuts to the width and thickness by which is more important to you. Test with the wheelbase blocks every step of the way!
So, yes… it will cut easily but slowly with a jigsaw. Use bi-metallic blades because PolyCarb is hard on blades. Because the PC is so thick you can probably use an aggressive blade. It also scratches easily. I like to put contact paper or shelf paper on the PC before cutting if it does not have a plastic coating already. Then I make sure there are no sharp areas where the jigsaw foot will touch the PC surface. Then I use furniture polish on the foot and PC surface so the saw will glide nicely. Then remove the shelf paper.
PC can easily be cut on a table saw with a using a fine tooth (60-80) carbide blade. As sl33py noted using a finer blade leaves a better edge is true. These are still rough cuts and honestly the cut marks remove easily by using files.
Making the board thinner - Most any plastic fabrication shop in your area can do this. They generally have large cnc tables. Note: A thinning cut on one side only may cause the PC to bend (might be able to use to your advantage) or make it flex differently on one side than the other when standing on it. Test it by using you wheelbase blocks and flipping it over. Have someone measure it while standing on it. To make it flat or eliminate the flexing difference, cut the same thickness off of the other side. Again, a reason to make small cuts.
Moulding the Board = Thermoforming: Thermoform after cutting. Use a phone book (I know, I know) to quickly find plastic fabricators and thermoforming shops. You can use an old wooden board that has the bends you want or make one out of wood. Again, be aware! Thermoforming may change the amount of flex of the board! Test it with your scrap pieces and ask the professional opinion of the shop. But don’t always believe what people say! Always test for yourself!
Again plan it ALL out!!! Just diving it and doing stuff it may end in disappointment! This is quite a technical under taking you are adventuring in. We are here to help!