What areas of the brain will Parkinson's disease affect?

The substantia nigra. Parkinson's disease destroys the dopaminergic neurons that live in a part of the midbrain called the substantia nigra (dark substance). The loss of Dopamine causes the basal ganglia to malfunction and this causes the slowness, tremor and dementia.
OK, here goes. Parkinson's disease is a problem of misfolded protein and predominantly affects the basal ganglia or striatum. Substantia nigra and other pigmented nuclei such a dorsal vagal nucleus and locus coeruleus are also afflicted. The dementia issues affect more widespread areas and this suggests that parkinson's disease affects more than dopamine.