In reply to CarolineMc:
Haven't been on Roraima itself but a few general tips may help:
When I was there earlier this year the currency exchange was insane, meaning that black market exchange rates were 10x official rates and illegal money changing was very common. Take lots of cash in dollars for everything and don't use cards unless absolutely necessary. There has since been talk of currency policy changes but I don't know if anything's actually changed yet.
Climate is very comfortable if you like being warm. Rarely does it feel stiflingly hot but higher up the bigger tepuis the temps can drop 10 deg or so due to altitude and often persistent cloud.
Don't take anything cotton as it will be near impossible to dry out if it gets wet.
Long bus journeys are actually very good nowadays - very comfy and can usually sleep at least badly! But make sure you have a fleece or a sleeping bag to hand as the a/c is often turned on high.
If you're travelling through Caracas - and particularly through the airport - be very alert. Once away from the capital things get much more relaxed and friendly. Sta Elena de Uairén is a great little town.
Have fun.