Sure you can create 3D models by simply typing the vertice and polygon information in Notepad. I've done that like 5 years ago too. You need to use a predefined format (like DirectX .x files) or define your own format (which is what I did).
Although it is definately possible, I do not recomment it. Creating a simple room and typing the values by hand already takes a considerable amount of time. Using a (free) 3D editor takes much less time. If you want to use your own fileformat, write a convertor to convert files generated by 3D editors.