In the first example (facades), my employer wanted to make a real-time version of the famous Barcelona's Barri Gòtic. We needed to model every visible building using max 700 tris each. I am building them into a render time scene and animating a camera, using low polygon modeling techniques, i.e. no subdivisions, curved surfaces base only on soft edges.
For the second study, I am using elevations and floorplans, high polygon subdivisions and sculpting (watch my Modeling and Concept Demo for more details). In both projects, I am using PBR materials for the textures (Texturing Demo) and lighting the scenes using skydomes with HDRI and directional lights. Using nParticles and volumetric lights to add some visual effects (watch my Visual Effects Demo), Maya Fluid for mist, paintEffects for trees and flowers, Maya Fur for grooming and grass, animated displacements for water and volumetric lights and flares. I am rendering using layers and passes and compositing using The Foundry Nuke (take a look at my Compositing Demo).