You have to open the assembly mode of Pro/E 5.0 and than Import all the component and then apply just simple constraint like Align and Mate to them.... This will make your assembly.
Also you gave to give any detail of what you have made so that it is easy to tell..
Before doing part modeling, untick the use default Template. and choose mm or inch..
ya i made the all the parts... but when i import it the size of the component is becoming larger than the roll cage... so i was unable to do if
check unit of your parts........