The trap shown above is based on a design by Bernard Skinner, the author of the first widely used guide to macro-moth identification. Like all the traps I use, it is a wooden box about 45cm square by 30cm high. As you can see egg boxes are an important part. They are put in the box for the moths rest in after they've come to the light.
This is it with the light on. You can see it has sloping Perspex rectangles meeting in a slot that it about 5cm wide. The moths attracted to the light end up dropping through slot. The lamp is a 125W mercury vapour (MV) lamp and it needs a choke (I bought the electric kit with the lamp from Anglian Lepidopterist Supplies). That's the expensive bit. Most of the wood I use I have found dumped to be thrown away. Extra cables are useful, so always save them from old mowers etc you throw away. I have put a small rain guard on it. It will survive light rain OK but with the sort of downpours we've been getting it needs a bit of protection.
The trap above is the same design as the first one but uses a 15W Actinic tube, this also needs a choke. I has the advantage of not being a very bright light, but it doesn't attract as many moths as the MV. It also doesn't run very hot so is OK in rain. The perspex is replaced by free ply, Perspex is very expensive. The disadvantage is you can't see in the trap, so careful opening is required. I normally use a netted gazebo, so that anything that escapes lands on the walls. I had to do this Even with the Perspex sided trap because I found I lost a fair few before I could identify them.
This is a different design, using a funnel instead of a slot. The bulb is a 160W blended bulb, it doesn't need a choke but runs hot and is sensitive to rain, hence the mixing bowl rain shield. I got the electrics and funnel from the E.L.G. (Paul Batty). All the rest came from scrap, except the Bowl and fixings.