OK, since lots of people might not know, a Tag Cloud is where you put a word in the middle and then all related words are placed around this word so that it looks like a cloud of words around the main word. Here is Wikipedia's example of a Tag Cloud:
In File Maker, you would have one table that has the main word and related to it would be another table with all the related words. This is a simple FileMaker relationship.
Now, having the relationship done is the easy part. How you are going to display it is a whole other thing. FileMaker's layouts are not designed for selecting random locations or locations of fields being based on the calculation engine. It is just not how FileMaker layouts work.
But, FileMaker can be accessed by other web languages such as PHP, or you can use a programming language that speaks XML or ODBC. These programming languages can write formulas for equal distribution of related words and their resizing and placement around the center word. Maybe you could get ScriptMaster's Groovy language to do this in a web portal, but that is the closest I can think of in FileMaker.
Basically, FileMaker is not designed to accomplish this task and there probably are better tools for it. Maybe there's an App for it?