Step 1: Find 3D models of your existing designs.
Step 2: Mix and match rooflines and parts, e.g. roofline of W205 and body shape of C117, and adjust size here and there.
Step 3: Apply different textures you find from Google Image Search to wireframe. In this example, skin some Acura lights.
Step 4: Apply for a job at Rockstar Games. I give you the new Benefactor Curbrasher, available in the next Soccer Mom Lease Special DLC.