Depends on if you want it to just look good or if you want it to be technically feasible from electrical, thermal, and manufacturing standpoints. Taking all of that into consideration would easily take 10-100x more time than just a novel visual prototype. Even look at Razer's triple-screen laptop from CES; they had one which worked, and one which looked pretty. Getting that last 10% of fit, finish, and feasibility takes a long time too.

If I used Fusion 360 (free for personal use) to design this, it would probably take me tens if not a couple hundred hours. Maybe you can get pre-made parts, like the memory chips, heat sinks and stuff.

Like another commenter said, fairly easy to do, but it takes serious time and creativity.

Why do people say this stuff is easy? It takes time and a lot of practice to understand the nuances of materials, lighting, how light interacts with various materials, cinematography, and not to mention the ins and outs of 3d modeling software.