It's not justifiable for your home builder to increase your construction budget by buying excess quantities of building materials.
But as life would have it, you must make the best of every situation you find yourself in. Instead of crying over spilt milk, here are three practical things you can do with the left over Perspex sheets from your home construction.
Lower Your Water Utility Bills
Metals (aluminium/steel gutters) exposed to water (rain) and moisture are vulnerable to degradation as a result of damage related to corrosion. Metallic gutters will often have to be replaced from time to time thanks to the damaging effects of corrosion.
Corrosion is a non-existent phenomenon for plastics. Thus, gutters made of Perspex would outlast those made of metal if all other factors that may contribute to gutter damage remain constant (e.g. strong winds and hail stones).
If your new home was fitted with gutters at the time of construction, you can use the Perspex gutters to create an additional rainwater harvesting system on detached structures around the home (e.g. carports or free-standing garages).
Harvesting rainwater reduces your dependence on the main water supply. This easily translates to lower water utility bills.
If you doubt your ability to transform sheets of Perspex into a gutter system, get your builder to do it. It's the least that they can do considering that he or she is responsible for your "Perspex woes".
Tag Your Dog
Your dog can be an unlikely beneficiary of your "Perspex woes". Name tags are commonly made of Perspex, among several other types of plastic. A name tag that includes details of your address would be especially beneficial if you have the adventurous type of dog who seems to be "allergic" to the indoor environment.
For the name tag, you'll need a scribing knife (available from local supplies stores), which will help you cut smaller pieces from the larger Perspex sheet.
You should first sketch the desired shape of the tag on a Perspex sheet. A scribing knife will "erode" the plastic material of the Perspex sheet as you press it against the outline of your sketch. You'll need to press the knife over this outline several times before the smaller piece is detached from the larger Perspex sheet. You can then use sandpaper (or a sharp razor blade) to smoothen the edges of the tag.
You should then use the knife to scribble out your dog's name on the tag. Add a dash of paint to the tag and you're done.
If you're not a dog person, you could make a desk name plate for yourself.