For conditional rules, you don't actually need to make sure that the else statement is reachable. The Colour rule with two case statements checking if Special is "N" or "Y" and an else statement is valid code and will run correctly. Since the range of the attribute Special is limited to either "Y" or "N", then the else statement will not be reached, but it is still grammatically correct code, and it will run as expected.
There are compile errors because of errors in the format of the conditional and stochastic (percentage) statements. In a conditional construction, there can be any number of case statements followed by an else statement, but the else statement must be there (with operations specified). Similarly, a stochastic construction must also end with an else statement. Also, the percentages in a stochastic construction must be <=100, and the else statement will get the remainder percentage to make the whole thing sum to 100. Here are the help pages:
Conditional Rule
Stochastic Rule
In your code on line 23, there is an else statement, which is probably intended to go with the case statements on lines 18 and 19, but the compiler thinks it belongs to the percentage statements on lines 20-22. Whatever follows this else statement is interpreted as the code that should be executed if this else statement were to be reached. Basically, to make the code work, an else statement for the stochastic construction on lines 20-22 is missing, and the else statement on line 23 is missing some operations after it (and similar for line 28). In general, if no operations are desired, you could write "NIL". Or, as Felix points out, you can structure your statements so that one case statement is for when area < 50, and the else statement takes care of the situations when area >= 50. I wrote this so that you could hopefully understand what's going on with the conditional and stochastic constructions, but you can certainly use Felix's code to solve your problem. However, note that you'll also want to make sure you account for the case where Height==12 by using the <= or >= signs in your conditions.