How do call a random .php file from another directory

I am trying to call a random .php file from a specific folder in my directory.

If I place the files in the main folder (root directory), it works fine however, My webpage will have to go deeper at some point so if I am unable to call files from any point in the directory, this could get quite messy.

So this works perfectly for me by having the files in the same folder

<div class="col-sm-3">                       
    <?php readfile(rand(1,99).".php");?>
</div>

However, when I try to place the random files into a specific folder (in the root directory), It does not return the .php file. I have tried the following

1. <?php readfile("/Myfolder/".rand(1,99).".php");?>
2. <?php readfile("Myfolder".rand(1,99).".php");?>
3. <?php include("/Myfolder/.rand(1,99).".php");?>

And all sorts of other combinations of ../ , "/ , ../../ etc

I also need to be able to call files from any point in the directory ie "../../"

I am new to php and this at the moment is really stopping me from progressing so any help in is very much appreciated.

Cheers