Good question sunflower. Which country do you live in; here in the UK we have local council planning and a quick phone call might put your mind at rest. A picture would help to explain better what you propose to do or a bit more detail please.
The first thing though is safety if removing a pillar because the pillar is usually there to hold something up; are you planning on creating a porch?
I recently made our own new front entrance to our bungalow and I tend to do things the hard way; I like timber but using plastic would have been a great deal quicker and easier because entrances can be bought ready made and installation is usually a two person job.
Here's mine but as I say I do things the hard way and I might have completely misunderstood your intention; I didn't need planning permission?