Use the Expressway gate and turn right onto Soi 38. Follow it around and take the last right turn before Chaengwattana. Follow that until you have to turn right (solid line). Park wherever you feel like you’re out of the way. Watch out for the chickens.
You’ll see the tall building on the horizon that’s Makro. In the far left corner of the courtyard there’s a walkway (the dashed line) that’ll lead you to a gate that’s open from 4:30 am to 11:30 PM. Makro itself opens at 6 am.
Hop through the gate and you’re right around the corner from the entrance. Note that the gate is narrow – so be careful that whatever you buy at Makro will fit through.