It's very easy to make your own concrete bricks, pavers or stepping stones. One item you will need is a form in which to cast your project. You may need more than one and you may need them in different sizes.
Let's use a patio paver for an example. Let's say your patio design requires cement stones that are 8 x 8 and 8 x 16. Here's how you would go about making these forms very easily.
Buy some cheap furring strips at your home center. These are eight feet long and 2.5 inches wide. Also buy some 2 x 2. It's also eight feet long. Get some coarse-threaded screws 1.5 inches long.
From this stock you'll cut two pieces eight inches long and two pieces 20 inches long for each form you want to make. You will also cut four pieces of 2 x 2 that are 2 inches long. The only measurement that has to be fairly accurate is when you cut the eight inch pieces. The rest can be approximate.
Put two of the eight inch pieces together back to back. Put two 2 x 2's at each end so it looks like a capital I. Now you know where the 2 x 2's go, take one eight inch piece and put it on its end. Hold the 2×2 in the place you just had it while you pre-drill two holes and attach the screws. You want the edge of the 2 x 2 and the end of the eight inch piece to be flush. Assemble the other three ends the same way.
Put the assembled pieces back to back again in a capital I. Spread them apart until you have a measure of 16 inches between them. Now screw the 20 inch long pieces on with one screw in the middle of the 2 x 2 so you miss the screws you have already put into it.
That's all you need to make your 8 x 16 forms. When you want to use the 8 x 8 forms, just unscrew the 20 inch side pieces and measure your 8 inch pieces to be 8 inches apart. Pre-drill a hole and screw them to the 2 x 2's as before.
If you decide you want an 8 x 4, you just slide the eight inch pieces to that measure. You could use this form for any 8 by "X" size brick from one inch to 16 inches.
What about the thickness? What if you do not want cement bricks that are 2.5 inches thick? There are two ways to handle this.
One way is to only fill the forms to the depth that you want your brick to be thick. You could make a sight line on the wood to know when you've hit the right depth. If your bricks turn out to be of varying thickness, do not worry. You can compensate when you lay them.
The second way is to trim the wood to the proper width on a table saw. If you have a table saw, you can use any wood you can find, even boards from old pallets will be fine, and save the expense of buying the furring strips.
Have fun with your project!