The shelves

Ingredients
The frames you’ve just made
Either 4.2m of 100mm by 22mm treated softwood or
2 of 3.6m 22 x 47mm yellow battens plus either 2 pieces of batten each 45 cm long or
1 piece of 100mm by 22mm treated softwood 60 cm long
30 of 4x40mm screws

Tools
Drill with 2.5mm bit
Screwdriver
Jigsaw
Saw

Method
Personally, I have always made my shelves out of 100x22mm softwood but two pieces of batten with a small gap would do instead of one piece of softwood.  The disadvantage is that the construction would take longer, the advantage is that, when you water the plants on your theatre, water would drain through the shelves more easily instead of puddling.

1 – using softwood – Cut the softwood into 60cm lengths.  The bottom shelf takes 3 of these, the middle shelf takes 2 and the top shelf takes 1. The 7^th piece is for a backboard to the top shelf which is not just cosmetic, it also gives lateral stability

The top shelf and the front pieces on the middle and bottom shelf are not easy to screw into place because of the angle of the front strut.  It’s much easier if you drill the holes at an angle and put the screws in before putting the shelf in.  Using one of the L-shaped attachments for drilling and screwing round corners might also help. 

The front plank of each shelf needs an angled “ear” cutting out of it at each end

2 – using battens Using battens instead of 100mm wide timber the only real difference would be in the lateral brace behind the top shelf.  It would look like this:

Oblique pieces of batten are fastened to the top of the rear struts and to the middle of the top shelf.  These are the two 45cm pieces mentioned in the ingredients.