Advice needed with for custom canopy

I have finally decided on a basic design for the canopy I want to build for my 600mmX325mm tank.
I know that there are lot of members who have done the same thing and need some help before going out and buying the wood.
What wood would be recommended to use for the sides (uprights) of the canopy?
I was thinking of going with PAR pine, either 12mmX96mm or 22mmX96mm .
I am trying to make the canopy as sturdy as possible, as well as trying to keep it as light as possible.
What wood would be recommended for the 'lid', some type of plywood or maybe marine ply?
How would I go about sealing the inside of the canopy? Should I just paint the inside white right over the bare wood, or do I need to seal it with someone else first?
Would it be necessary to have fans mounted in it to deal with the condensation? If so, where would the best place be to mount them, on the sides or on the top?
TIA.

 

Pine or Meranti would work, just remember to varnish well. First layer of varnish should be diluted with thinners to help the wood absorb it, then just give it another few coats.

 

Do I varnish the inside and when dry, paint white over it?
TIA.

 

Any other comments or suggestions?

 

No - paint and then vasnish - although I would use an oil based white paint for the inside of the lid - it is water resistant and pretty shiny too if you use the gloss. The only thing is that you have to use a wood primer otherwise it might flake off.