My miniature airport vehicles are all designed for 1/400 scale so they can only be printed in "frosted detail" plastic. Often the price difference is less than a $1 between the materials so I don't even list smooth plastic as an option. You can message and request other scales but only 1/144 and larger might have a chance to be printed in the cheap "versatile" plastic.
The software I use is Solidworks and is geared toward industrial design like the things you see in my store. You can see my portfolio at facebook/ttakata73 (I don't use FB's messenger). Any basic design needs to have a front, side, and top view. If the bottom and back are different then those drawings must exist too. I essentially need to know what an object looks like from all sides so if you don't have this info I can't make it without a lot of guessing. You can find great videos online about "orthographic drawing" to explain how to design on paper. I don't do sculpted forms like modern cars because no info exists for body contours so they would be impossible to duplicate without a 3D scanner. You should be realistic about pricing objects. I wanted a small 1/400 building printed but when the price was $900 I lost interest.
My design rate (if available and interested) is $50/hour.
Example1: 1/400 TaxibotWB took 20 hours since no drawings or dimensions are publicly shared.
Example 2: 1/400 GPUFT99 took 2 hours to design since its made of simple extrusions and drawing/dimensions do exist online.
Please email any drawings to ttakata73@gmail if you want a quote.