For the service bay, I would allow a 6 foot working area/path on each side, front and back of a full size auto, this should provide ample room for toolboxes, engine hoists and car doors. The 12 foot ceiling sounds about right, but you may need to close the hood before lifting the car.

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'87 190E 2.3-16
Heated Seats, Graphite Dash,
Delsing shift bushings