Squares and blocks and pyramids are all fine and good, but there will be times when you'll want something to be round, even more round than an octagon.  Unfortunately, round bins, per se, cannot be made.  The workaround is to create a model that has many sides, each one rotated or angled slightly more than the rest until the last one comes full circle and meets the first.  This is how tires are made (tires are just a lot of small faces joined so that they form a circle).  The exact number of sides will depend on the overall size of the model (less sides for smaller models, and more sides for larger models). The smoothing in the game will take care of the rest.  You will, in effect, have a round model.

Creating circles is easy if you follow a couple simple formulas.  The angle of rotation is calculated like this:  360 divided by the number of sides you want for the model.  For example, a sixteen sided model would use sides rotated 22.5 degrees from each other.  But a simple rotate-insert-rotate-insert method wont quite get you there since the sides will not line up properly without some adjustment.  The translation is calculated like this:  Find the vertex coordinates of the points you want to line up, then subtract or add the coordinates of the model you want to move from or to the model you want it to join.  This will always involve a two axis translation.  This is not hard to do (rotate-tranlaste-insert-rotate-tranlaste-insert), though you might want to practice it a couple times before altering the model you are working on.  You may also use this method to create arches or partial circles.

Stop.

Whether you find this discussion easy or difficult to follow, I will not attempt to clarify it with diagrams and more explicit demonstrations of the math because there is an easier way to create round objects.  TireMaker by Bin Masta is a DOS based program that makes this task as easy as can be.  Don't let the name mislead you, TireMaker might just as easily been named BinMaker because you are not restricted to tire shapes.  You can use it to make round objects with every possible contour you can think up.  For example, the new and improved mtm1 fire hydrant was created from two round bins made using TireMaker that were then mapped, resized and  inserted into one another (forming a "t" shape) in BinEdit..
 

Three final notes on TireMaker.

1. This section of the Guild is dealing with BinEdit.  I will not expand on using TireMaker here.  There is an excellent readme.txt file included in the TireMaker download zip.  Please see that for specific instructions on how to use it.
 
2. If you try TireMaker and like it, please send Bin Masta a note and let him know what you've made.  I am sure that if he sees enough interest in his program that he will write an updated windows version that, who knows, may even allow you to preview the work before saving.

3. The TireMaker homepage is here. And the mtmg's TireMaker tutorial is here.

Yes, round models are possible in BinEdit, and I hope I have provided a clue toward figuring out how to make them.  But I can see no reason why anyone should want to go to the trouble of all those calculations when TireMaker is available and easy to use.

Finally, there is another lesson in all this:  BinEdit is not the only game in town.  Yes, it's probably one of, if not the, best programs for mtm2.  But there are others.  The bottom line is to do whatever it takes to improve the quality of your tracks and models.

And don't forget to save you work.