I have a garage which i would like plastered and was wondering if it will have to be rendered with sand and cement or could i have walls boarded and skimmed over with plaster???

You can either render or fix boards, although personally i would use plaster boards as this is quicker and less messy. You could dot & dab but make sure you use a good adhesive and space evenly over the wall, ensuring the adhesive covers all corners and edges to ensure strength and consistency. Or you could attach 4"x2" timber battons to the walls then fill the studwork with 4” cavity insulation and attach moisture resistant plaster boards. Hope this helps.

Presumably you want to use this as some kind of room then and its not just to house the ferrari? You can board and plaster but its not as simple as just sticking the boards on the wall if damp is likely to bother you:) Have a look on the internet at garage conversions.You dont have to go the full extent if its not a building regs thing but it will give you an idea on how to finish the walls in the right way and give it something in the way of insulation.If its purely to hide naughty blockwork,you can cover it in any way you want.

yes you can just board and skim without rendering

yes you can you can dot and dab your boards on the wall just dont put them on the floor a inch batting will help you on the floor that will not bring damp up but take the baton away