Just at a glance this looks like it would take a half a grand to make on the cheap.
I would not recommend a costume like this for a first time build. It would take a lot of time, and resources. The amount of effort you would have to put into a costume like this would require a lot of dedication to finish. You may even have to ask yourself is it worth it?
Is this just something to wear a couple of hours at Halloween? Or something for a film, or competition that you really want to impress people with?
The amount of time put into a design like this would be the deciding factor on how good it looked. You could spend 4 hours on it and end up with a junky costume. Of you could put 4 months of work into it and have something that you could film for a movie.
If you can not sew buy what you can. Either at the store, or online. You can modify clothes you find at thrift stores too.
Then you can focus on the things you will have to make. The two methods people choose are sculpting, molding, casting? Or fabrication out of foam, worbla, or plastic/ wonder flex.
When searching on how to make something don't look for just ninja costume builds. Try researching people's armor builds to see how they created their shin, and arm guards. They may not look exactly like the ones you are making but the same methods could be used.
Example.
http://www.therpf.com/f24/diablo-3-female-barbarian-tier-5-armor-build-204076/
Here is a video that runs through how to use foam mats to make armor.