Making site models tends to be fairly easy once you’ve got the hang of a few pretty straightforward commands. The tricky bit is always the topography if the site is complicated. I’d suggest just assuming the site is essentially flat while you get the hang of the basics.
You could add things like the canal in due course.
In terms of extruding curves to make buildings, I would suggest making sure the outline of the buildings in plan are closed curves. You can do this by selecting the curves (what rhino calls lines) that make a single building and using the
join command. You might have to tidy up the curves so that they make a closed curve, ie a continuous loop.
Once you have that, use
extrudeCurve to your desired height. You should select the option to make it a solid which just caps the top and bottom of the extrusion. If you forget, you can use the
cap command to do that afterwards.
Obviously, once you’ve got the basic massing there, you can work into it as much as you want (or can!)
A building with more complex geometry will always pose a bit of a challenge and may require investigating and learning some other tools.