I see! You could still use the desktop version and see if theres a model that might help! try looking up something like, "class" etc! you can just take a screenshot and use it as refrence if you find a model with a floorplan similar to yours
Another thing worth trying is, if you are using clip studio paint you might found some free assests/3D models ! even the ones that arent free are really cheap, you can get them for a dollar or two.
As for your existing model - it looks good! It depends on which angle you want to show it in-comic though, you could also play around with the free tranform tool to add more perspective to it c: