Your preview already looks like a mesh.

If you are comfortable with sharing your data please supply a sample .shp file.

sorry, I sort of meant to say if there was a way to optimize this .shp file. I thought I would need to turn the .shp file into a mesh to use meshsimplifier in workbench.

Use a Triangulator - and from the TINSurface output use a MeshMerer to merge the mesh features. You can use the Groupby function to in the MeshMerger to keep each building as individual meshes or merge the whole thing into a single mesh. You should then be able to use the MeshSimplifier. Keep in mind that while FME Will try to preserver the shape, the shapes of the buildings will likely change as there will be less vertices.

This almost works with my data, for some reason there's a problem from the Meshmerger to meshsimplifier. I wasn't sure how to group them into one mesh so I chose group by: FEATURENAM and fme_feature_type. Im not quite sure what went wrong

Hello @jaronkasiban​ , the MeshSimplifier requires that the mesh be manifold. Manifold meaning all one piece, with consistent face normals, and edges-matching-edges. Unsure your data meets this criteria as it is many separate buildings. If you had a building_id or the equivalent, you could create a mesh for each building and then individually simplify - as previously suggested by Matt. This may not be the best approach if there is excessive triangulation in the buildings. Hope this helps, Kailin.

Hello. I'm having almost the exact same issues. I have a shapefile with some 3D buildings and when I read it with FME, instead of just having rectangular surfaces, I get triangular faces. So when I try to export the data to a REALDWG format, I get a lot of extra linework that the client doesn't want to see in the wireframe. I've tried some of the solutions mentioned previously and I get to the same point where I get an error in the meshsimplifier that says INVALID_MESH and I also tried the surfacedissolver which didn't do anything. The first image below with the black background is what my dwg file looks like when write. After I use a Mesh Cleanup tool in microstation, the second black background image is what I want with no triangles, just surfaces.

Above is the shape file in the FME inspector

Above is the output REALDWG with a lot of extra linework.This is how I want the buildings to look in the REALDWG