Firstly does jumpstartng my mates car run mine down? I have rain seeping into my boot from a gap between the canvas roof & rear of car. Like the roof has shrunk. Do I need to replace canvas roof?

Using jumper cables is for emergencies only- not for daily practice- every time you do it, you risk damaging your car and serious personal injury-to minimize the danger to yourself, ALWAYS connect the positive cable first- then the negative- this cuts down on the chance of a spark, which can create an explosion of battery acid- when the 2nd car starts, IMMEDIATELY disconnect the cables, starting with the negatives- when two engines are running and charging into each other, there is a chance of damaging diodes in the alternators

I stated the basics, but here's a coupla other tips for safe jumping- for even greater safety when connecting the cables (+ first - second) make the last negative connection not to the battery but to a piece of metal under the hood that will ground without being around the battery- even less chance of explosion- AND with the cables connected, turn OFF the engine in the car with the good battery, THEN try to start the dead car- people always think the car has to be running- NO- a good battery will start a car even if it's not in the car- this cuts down on the chance of two running alternators tryin' to blow each other out