Roof Panel adjustment procedures from the GM repair manual:

There are five adjustment procedures for aligning the roof lift off panel. Perform the appropriate adjustment(s) as necessary:

1. To adjust the front striker perform the following steps:
1.1 Loosen the bolts and reposition the latch striker up or down for major adjustment.
1.2 Loosen the striker outboard bolt and pivot the striker on a slightly loosened inboard bolt in 2 mm (0.08 in) increments for minor up or down adjustment.

2. To adjust the front latch handle, perform the following steps:
2.1 Loosen the latch handle bolts
2.2 Reposition the latch handle forward or rearward. Maintain a minimum of 2 mm (0.08 in) clearance between latch handle and the latch striker to avoid squeaks and rattles.
2.3 Assure the latch handle base is parallel to the striker to provide clearance to the sunshade mirror door.

3. For major rear latch adjustment adjust the rear latch striker performing the following steps:
3.1 Remove the roof lift-off panel.
3.2 Remove the roof bow center interior trim panel. (Refer to Trim Panel Replacement - Rear Roof Bow in Interior trim *PM me if this is needed)
3.3 Loosen the rear latch striker attaching bolts.
3.4 Adjust the position of the latch striker forward or rearward for major adjustments. (Notice Refer to Fastener Notice in Cautions and Notices - * PM me if this is needed).
3.5 Tighten the striker attaching bolts. Tighten the roof rear striker bolts to 10N.m (89 lb. in).
3.6 Install the roof lift off panel.

4.0 For minor rear latch adjustment adjust the latch handle hook on e turn at a time to achieve moderate pressure to the latch as follows:
4.1 Remove the roof lift-off panel
4.2 Loosen the set screw locking the latch hook
4.3 Turn the hook in to tighten or out to loosen.
4.4 Tighten the set screw
4.5 Install the roof panel.

5.0 To adjust the rear locator, perform the following steps:
5.1 With roof installed on the vehicle, loosen the locator mounting bolts.
5.2 Reposition the locator.(Notice Refer to Fastener Notice in Cautions and Notices - * PM me if this is needed).
5.3 Retighten the mounting bolts. Tighten to 10.N.m (89 lb. in).