LeWitt's wall drawings are meant to be ephemeral, and the ones I saw on display were going to be painted over later. They are given as instructions for a draftsperson to execute. You can find examples at http://massmoca.org/sol-lewitt/ or http://www.ericdoeringer.com/ConArtRec/LeWitt/LeWitt.html
The instructions are somewhat terse. For example, Wall Drawing #104 is simply "Arcs from the midpoints of two sides of the wall." But, it looks like most executions do not actually engage with the freedom this provides. They instead more or less follow the initial interpretations and the conventions implied by other drawing instructions. For example, the standard interpretation is that the drawing is black unless specified otherwise. The draftsman ensures that lines or arcs are evenly spaced unless they are "not straight" or explicitly "random", and that they intersect the boundaries of the figure. This is an "originalist" reading that says we follow LeWitt's earliest examples if the text is ambiguous.
Unless, of course, you let the museum visitors try their hand. Then you get variety: http://risdmuseum.org/manual/45_variations_of_a_drawing_sol_lewitt_and_his_written_instructions Of course, some of this variety is "I want to draw Snoopy rather than following these stupid instructions." (Even the examples there assume that the basic topology of parallelogram-inside-circle is specified. But is it?) Which is more in the spirit of "conceptual art"? The RISD museum decided that the text was insufficient:
These differences made clear that despite LeWitt’s desire for objectivity, a great deal of subjectivity exists when others are involved in the making. LeWitt certainly was aware of the variations that might occur, and although he might have accepted that his instructions could be drawn a number of ways, he did have preferences as to how his works were installed. That’s why, rather than using the written instructions as the sole guide for installing the wall drawing at RISD, the Museum’s installation crew was assisted by draftspeople from the Sol LeWitt Foundation who provided a diagram to help LeWitt’s idea take form.