It's usually after I change or modify something in the frontend that would affect the suspension's ride height that I check the alignment (or if I notice the steering wheel position has changed).
As for DIY alignment tools, you just need a tape measure (or a telescoping rod that'll fit between the inside edges of the front rims), a steel plate & some small round metal dowels to put under one front tire (so there's no tension between the two tires that would affect the suspension's height), a piece of wood that's similar height for the opposite tire, and a working knowledge of how to adjust the alignment (caster, camber & toe). You'll probably want the 2-piece fully-adjustable bushings if you're doing this "at home" too, as some trial-&-error may be needed (fixed-degree bushings are impractical to use without a computerized rack to tell you what your current specs are).
