The big issue with big band saws is that the column twists when the blade is tightened. This is what separates the good Italian saws from the cheap Chinese ones. When you tension a good saw, the column will bend in a vertical line with no twist. In big band saws, it is all about the column.
A 14" vertical is something like a 20" or bigger band saw. This is a pretty big machine and the blade will be running upwards 150" or longer. This is a whole different world than the little crapsmans or deltas.
Tensioning even a thin kerf blade that long takes a boatload of force, even more for bi-metal blades. If you hope to put brazed carbide blades in it, or run a blade wider than 5/8" it will look like a banana when under tension with a 2" square column.
There are plans out there for shop made saws, some of them are pretty good. Keep in mind that this is a big expensive project, there is no reason to spend the time and money for something that only "works well enough." Make it right, make it strong.
I can see welding 4 pieces of 2" tube in a square column, this might give the required rigidity. You would want continuous welds so that it will twist (meaning no twist) uniformly. I would be more inclined to get a piece of I-beam, something like 4" x 6". I might even be tempted to weld plates onto it to make a box column with a web inside it. It is much easier to overkill the column, than it is to try to design around twisting, upper blade tilting can only compensate for so much. A saw whose wheels go out of being co-planer under tension is almost worse than useless - it will never cut right, and you will hate doing simple things like blade swapping. On my saw for example, it takes me less than 5 minutes to swap from a 1/4" blade to a 1 1/2" carbide tipped blade, and most of that time is adjusting the guides.
Beyond that, some random thoughts:
Scrounge up a used portable table saw or an old 8" table saw for the table. The saw hole will need to be filled with a plate, but you get ready made miter slots and fence. An old 8" stationary saw will have a cast iron table and trunion, look for an ancient craftsman. If you get a cast iron trunion, you should be able to repurpose it for the table tilt. A cast iron table will also tolerate the split, and alignment pin needed to install the blade better than an aluminum one.
Take the time to put hinged doors on it. Screw on covers are the suck.
Multi-speed it good.
Cast iron wheels are the best, next is cast aluminum, distant last is anything else. It will be worth sending the wheels off for reconditioning if you can score used ones. I would be more inclined to have someone cast me wheels from aluminum than to fabricate them from steel. Get some cylinder heads from a BMW or Mercedes from the junk yard - they are made from really high grade casting aluminum, and should cost the same as any other head if it is scrap.
Front wheel bearings from a front wheel drive car might be a really good choice for the wheel bearings. Just ask for what it cheap and design around them, they are designed for this type of force and will be much cheaper than getting them from a machine dealer, not to mention simple to install.
I prefer an upper wheel tilt mechanism that pulls the top of the bearing mount to one that pushes the bottom, they are a bit easier to fine tune.
