How to construct a new cage level?

[gogoguineas]

As it says, I'm trying to work out how to make an extra level for my boys cage. They have one like (can't find the original picture) this but the next size up (5ft by 2ft i think) http://www.zooplus.co.uk/shop/small_pets/hutches_cages/guinea_pig_cages/120_cm_cages/95868

But the plastic hidey thing is only used for sleeping, they never climb up top and I think its because its steep, so i thought I could make a level and put a ramp up to it, not too high of course, maybe a corner one even. I have some cosies on order from Laura and they have other stuff to sleep in so I figured this would create more space. My boyfriend is a carpenter so he is going to ensure the ramp is super duper.

But I'm unsure how to make it, any ideas? :{

 

[happyasapig]

i have 2 idenical cages, 1 day i will turn them into a double,ive measured them and if you hacksaw the top of the other should sit snuggly in it held by the lip of the base, it means the lower 1 is about 5"shorter but that will be better for the ramp hight ,then put the play stuff at the top to make them go up.......... i have the feryplast cages and if measured right will work perfect without using bits of wood supports