How can I build a shelving unit like this?
I found a matching image at http://www.furnitureinfashion.net/beech-home-wall-shelves-lasse-p-6628.html?osCsid=cf4c725a6d1c4b00d50adca495f827d3 which has dimensions of W85cm x D16cm x H47.5cm.

As to building it, I've built several like it over the years, and believe it really is up to you. What I mean is you can take this basic design and modify the dimensions to suit your taste. I use Excel and scale my plans until I'm satisfied before I even buy the wood. Also, you can build it out of any number of materials including: plywood, MDF, and solid wood. Also, the way you put it together is often dictated by your tools and skill. If you are a beginner and want to stain it, I would suggest you go with solid wood. It will be more expensive, but will simpler to build. I would also suggest you go to your local Lowes, HD, etc. and look at their selection of wood and see whether they have a hardwood you like. Looking at the picture, it looks like it veneered to resemble maple. But, I wouldn't recommend you use maple as it is too expensive. See if you can find another hardwood (I wouldn't use a softwood) that you like. 

Another thing that will dictate your plan is what type of saw you have and your previous skill using it. Ideally you would want a table saw or radial arm saw for the cross cuts. If you don't have one of these, or have no prior furniture building experience, I'd recommend you either buy a pre-cut kit (if you can find one), or find a local woodworking business to cut them for you. Otherwise you'll likely end up with misaligned or uneven cuts that will detract from the appearance.

I don't want to sound negative, but, to me, even though this may look like a simple project, it's not a beginner project unless you can be satisfied with less than perfect work. If you do decide to go ahead though, just don't expect it to be perfect or you may be disappointed. Just enjoy the journey and hope you get to where you want. Also, there are tons of web sites that provide free info on cutting and assembling bookshelves. Although they won't look like this, their planning, cutting, assembly and finishing techniques will give you the knowledge you need for the project.