Bear in mind that it's much harder to convert small track plans from larger scales down to Z. The problem is that track geometry becomes critical in tight spaces, especially with respect to switches. Other scales have many switch sizes with which to work, whereas in Z we only have a couple. It's far easier to scale down room-sized layouts for Z because you have wiggle room to make adjustments.
For scaling down from other scales, large plans or small plans, I recommend being a little loose with the scaling factor ... for example, use a divide by 2 factor for HO to Z scaling (as opposed to divide by 2.53) as it helps to address the potential tightness issues that David mentions and besides it adds a bit more spaciousness to the layout while still being a substantial savings in space.
For N to Z, I recommend dividing by 1.25 (as opposed to divide by 1.375).
Last night in chat, it was brought up about some new Z scale layout designs using MTL track pieces. David Smith has designed 18 Z scale layouts with the smallest layout being 20" by 36" and the largest layout 24" by 80". I think he hit the mark for the Z community. One of the biggest weaknesses for Z scale is that there really is no layout book like other scales have. I really think this is a must have bookmark:
And just as a reminder we have over 40 links to many Z scale sites. This is something we started this past August. If there are other sites we should link to, let us know.