While I think you can go a long way with site plans and SU, I think that you as a Civil engineer should look at discussions on inaccuracies within SU. For example you cannot draw a "true" circle. Just search "accuracy" or "inaccuracy" on these forums. For CAD you might look at Draftsight or DoubleCAD. I don't use them but they are cheap and seem usable. You are a little early, as Trimble is buying SU, and perhaps some capabilities will be added in the Civil direction. Sorry Gai, but the right tools for the right job, as it were.