Link Recommendation: Designing your own workout

There are two very useful articles out there about designing your own workout.

The first article is the more basic of the two. It's by Mike Robertson.

Program Design 101

The second article is more technical, but also a broader look at the subject. It's by Steven Low.

How to construct your own workout routine v1.2

It's a very detailed writeup. It's not as tied to "pumping iron" as the Robertson article; really, you could use it to design a training schedule for almost anything.

Both of them are useful, but both of them require some basic knowledge of the subject of training. I wouldn't recommend either as a starting point unless you're basically familiar with gym training in general and familiar with physiology. But if you're already on the way and training, either of them will expand your understanding of what goes into a program.