The second level has 90 + 8 = <<90+8=98>>98 parking spaces.
The third level has 98 + 12 = <<98+12=110>>110 parking spaces.
The fourth level has 110 - 9 = <<110-9=101>>101 parking spaces.
So the parking garage can accommodate 90 + 98 + 110 + 101 = <<90+98+110+101=399>>399 cars.
Thus, the parking garage can still accommodate 399 - 100 = <<399-100=299>>299 cars.
#### 299