Hello
Been using the package since 1996 in South Africa and have no regrets.
A quick answer to your question:
Roofs - Archicad can easily do complex roofs.
Site plans are no problem - The package goes further. Contours, cuts, fills, levels are not just 2d items but virtual model/site, so you can deal with the site as you would a real site or model. If you cut a section through a site, you get accurate information.
Customisation - Custom doors and windows are quite easy to do. For starters almost all doors, windows and objects included in the Archicad package can be easily adjusted to local South African conditions. I found that I've had to make very little customised items. However to make it even easier, the local distributors in SA bundle the package with many of the standard windows, doors and other objects as well.
My suggestion would be to contact Andre or Gideon at the TotalCad Solution Centre (031) 332-9448 (or check at archicad.co.za) for some info regarding tutorials. If you want, I can answer some of your queries directly as well. I'm in Pretoria, so if you're close, you can pop in.
Haneef Tayob
Aziz Tayob Architects
AC23 INT rel 3003, OS X 10.14.6 iMac 3.3ghz i5 dual monitor, 24GB RAM