Re: Will a piggy fit?
Are you asking about the loft being a 1.5 x 4 or the cage base? If you mean the whole cage, most of the people on this site are going to say the minimum width should be 2 grids wide. Can you measure your space and see what the exact dimensions are of the area you want to put the cage? Maybe if you do tie wrapped grids and no connectors you could fit 2 grids across if you are only short by a little bit... Also, you don't need to cut the grids to make the cage narrower, you just overlap them how ever you need to and then cable tie them together. If you absolutely can't fit more than a 1.5 x 4 sized cage, then a this site suggests a single loner female (a female who does not like to be with other pigs) would be better than a male. Or two already bonded small females would probably work. Some pigs are much bigger than others. This site wouldn't recommend trying to put two boys in such a narrow cage. I have seen plenty of people on other lists house bonded boys this way in smaller cages though. I think it really depends on the pigs.
If you are saying you want to do the loft the longer way and make that 1.5x4 I think that would be pretty cool, a bit more time to clean because your loft tray will be pretty big and kinda awkward. As for wonder bars, so far as I know the only place that sells them is the cage site. They are 7.99 each and come in black and white:
http://www.guineapigcagesstore.com/candc-wonder-bars#.UjWscRafdhA
I really, really like them but if you prefer to shop locally...Then you would probably have to look around and see what you can find. Most likely it would need to be wood instead. You might be able to run wood the long way across (so it is a little longer than 4 grids wide) and still have it be stable, you would probably need thicker wood or wider dowels to do it that way.
If you are ok with ordering from the cage store website, I will suggest that you look into their coroplast bases and they can also custom make you the loft. Their shipping seems to be about the same for the wonder bars and for bases. I really like ordering bases from them because they do a really nice job cutting and scoring. I would start with their bases and when you need to replace it use that for a template for any replacement bases you need. Also, I highly suggest using velcro to do the flaps on the base instead of tape because then you can open it up and clean out the corners if you need to.
As for cutting the grids, I haven't done it before so maybe someone else can answer that. If I was going to cut my grids I would use wire cutters for the inside thinner wire and a saw for the thicker wire. Possible tin snips could cut it but I don't know. If you have the space to do it, putting the ramp across the back makes it the least steep.