Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: 1) is the build plastic and metal base or metal and metal?2) Is this OK for portraiture?
Document: For those familiar with the Pentax brand, for years, Pentax has specialized in small, tightly built primes. Those with all metal builds are called the limiteds. For whatever reason, the D FA 100mm WR does not receive this designation, but it certainly fits with the overall theme of both the DA and FA limited lenses.Build is metal and very sturdy. Hood snaps into place and is fairly good sized. Lens does not have an aperture ring or a focus limiter. It does have quick shift capability which is very handy and can limit hunting.
Top notch quality lens, small, compact, elegant and very well made. The metal build and high tolerances are very close to the standards one has come to expect from the Pentax series of limited lenses. Optics and performance are excellent, and the weather resistant design certainly adds to the value of this lens. Unfortunately, the autofocus is less than perfect --the absence of a focus limiter for me is a perceptible drawback, since hunting happens frequently and takes an annoyingly long time. This of course means that for moving subjects manual focusing becomes necessary, something that might not be a deal breaker for some but that for me takes away from what could have been an almost perfect macro lens.
It was a tough decision between the famous Tamron 90mm f2.8 macro and the new Pentax 100mm f2.8 macro. Decided on the Pentax  despite ~50% higher price: WR, 49mm filter, lighter and more compact, all metal outside, excellent sharpness across the field and one stop down from 2.8 (still very-very good at 2.8, compare the graphs for the Tamron and Pentax on LensTips). The fact that protruding front lens is completely hidden inside the hood makes it very handy for street-candids-portraits.
I like my K5 but I have not bought any new lenses other than the 18-55WR that came with the Camera. I have some Film Era zoom lenses, a FA50 f1.7 prime, and some manual focus primes as well as 3 other Pentax Film bodies. The FA50 is good glass, the other primes are OK glass, and the zooms are a mixed bag.Now this lens, 100mm f/2.8 WR, well it is Terrific Glass (I need a stronger synonym but I am too lazy to find one right now).
I used to have the older version of this lens and it was one of my favorite. I love shooting flowers up close and the 1:1 macro lenses are excellent for that. In December I decided to sell my old one when I picked up the Limited 35 mm macro. I love that lens too but it doesn't get close enough for the way I like to work. Now that spring is here I've picked up the new weather sealed version and it's pretty fantastic.The bokeh is soft and very pleasant, maybe even better than the older model.
The better build quality and weather resistance were worth sacrificing the aperture ring for me.
This lens was designed using top-notch technology with photographers in mind. Minimal weight, nothing sticks out, the focusing ring is at the end of the lens, an additional central groove makes it very tactile - easy to find w/o looking and easy to turn w/o slipping - it just "sticks" to your fingers.The lens is really compact and sits well on K-5, easy focusing. Sample pics were taken handheld 1/500 around 6pm under partially cloudy sky with AWB.I don't miss the aperture ring but I would appreciate a focus limiter (was focus hunting 3-4 times out of 50) and slit in the hood for CPL.
Small yet you can feel the quality. The IQ is stunning. I just love metal lenses. It feels just like one of the limited lenses.Excellent buy. Highly recommended.
If your running Pentax - this is a great lens. Note - prices are going down here in June 2012. Excellent macro capability, fantastic color rendering, tack sharp and metal construction makes it an all around great package. Pentax makes some fantastic lenses - and if you are using their system - this is a great lens - especially with a weather resistant camera like the K7, K5 and the upcoming K30 - this is a great compliment for a good weather tough package. 100m focal length is a bit strong tele on crop sensor - but this lens works well for a prime.
The build quality of the new lens feels a lot sturdier than the old one. These macro lenses protrude a long distance from the body when they are close focusing, that hasn't changed between the two but the WR version feels more solid.The new lens hood is a tad smaller than the old one which makes it easier to carry around. I think that it's the same length but the opening facing the subject seems narrower. The lens motor is not the SDM variety, like the "star" lenses, so it's not whisper quiet but it's no louder than the old one.This new version does not have an aperture ring so I don't imagine that it would work well with an older camera body but if you have a modern Pentax DSLR I think that it's a good upgrade.
Answer: It is primarily a metal lens.  There maybe some internal parts that aren't metal or glass, but it is metal on the mount and exterior.  I would say that it is a good focal length for portraits, but is a little sharp for such a purpose.  Of course, you could always soften things in post.