The frame and shed of the wagon are already one. Next in line are the parts of rolling and braking system.
You need to prepare a file with vector drawing of parts of the model in proper scale.Like here below
Red line means markings for laser and black line are for cut.
For create file you must use some CAD programs (AutoCad, Rhinoceros, or free DraftSight etc.) or CorelDraw.
On the edges of cuted items should be left so-called feet with a width of 0.5mm the items will not fall out of the sheet.