The question of artwork and its various options always confuses people and every print company does it differently but this is a bit of information to perhaps help you to decide what you actually want in terms of quality and why. So typically artwork is created on a computer with a small screen which then needs to be blown up and printed on a big printer. A couple of considerations when determining quality: 1. how big will this be when printed 2. how close will anyone get to it. So if the closest anyone is going to get to it is 100m away, it can be very low resolution and still look flawless from this distance. By comparison, if its a wall covering on an exhibition stand where people and products are going to be right next to it, you probably want to have the resolution as high as possible.
Store all of the above and we will come back to that momentarily. The next consideration is whether you use (or are able to use) vector graphics or raster graphics in your initial creation of the image. The two are created very differently and scale up in size very differently. A raster graphic is the most common type. It is millions of little coloured dots (or pixels) all grouped together to make up the image. Interestingly this is how an inkjet printer also prints the image, by printing millions of tiny coloured dots to make up the image. If you design a nice raster image on your computer and then scale it right up, you actually do this by just making each of the dots bigger. So on your computer they may be the size of a speck of dust but if you scale it up enough, to cover the side of a building for example, each dot may end up the size of a 50p piece by the time you are done and look very blocky when up close. Resolution is measured in dpi or Dots Per (square) Inch. When you create an image, you will tell your design program what dpi you want to work to (300dpi or 600dpi are fairly common). The more dots you cram into each square inch in the design, the smaller they are and so the smaller they will be in the final print when you blow it up and therefore the higher the resolution of your final print.
The down side of higher resolution designs of course is that file sizes go up meteorically so frequently you will create a design and then perhaps have to send it to your printer as a scaled down version of the original because its just simply unworkably big. This of course means your intentions of high resolution go out the window but thats the balance that needs to be struck. More dpi = more pixels = more dots of colour information to store therefore more data and larger files.
The final piece of this jigsaw is the vector image. These are particularly good for logos and designs but don’t really apply to photograph based images. Imagine you have a line from point A to point B on an image. This would be recorded in a vector image as “Draw a line, 1 pixel wide from 0 to 10” The joy here is that if you scale this vector image up, you just change the instructions. So to get a line which is 10 times the width and length, the imaging program just changes the instruction to “Draw a line, 10 pixels wide from 0 to 100” So two things of benefit here. 1. you can create a drawing on your computer with its small screen and then scale it up to any size without losing any quality as the printer just prints the instructions with a nice sharp edge and 2. the file sizes are very small by comparison as its just a series of instructions rather than data on the colour of every pixel on the print.
Combine this with the questions of quality in the first section and you can make an educated guess on where to start your design quality.