If it's got a ladder, it's not a proper loft conversion and you can't officially use it for a bedroom or the like. Legally converted lofts conform to all manner of building regs such as proper stairs at no more of an angle than x degrees (I think it's 45 but I could be wrong), fireproof doors on all rooms leading onto the stairwells, an emergency exit from the loft out onto the roof (and I don't just mean a Velux window!), proper support under the floor to support real weight (normal ceilings are likely to not be able to support a large bed with occupants), etc.
I had mine done and I have massive JCBs bridging the outer walls and a proper stairwell. It costs real money to do it properly in such a way as to be safe. Do it without due respect for the regulations and if you end up falling through your ceiling, don't expect your insurance company to pay up!
And if you're buying a property with a conversion, make sure you see proof that it conforms.