Mechancial engineer graduate whats best choice for me

I have 2 offers 1 grad scheme which is in material procurement which has nothing to do with engineering and another role a shift engineer where I’ll be looking after maintaining and working and understanding building mechanical systems my career goal is to land a role as a mechanical engineer graduate scheme whre I will be designing buildings and stuff the material procurement is a 2 year contract and the shift engineering role is through an agency so I can leave whenever what should I do

I'd take the shift engineering role since it's an actual engineering role and seems to be directly relevant to the area of engineering you want to enter. Procurement is a different career to engineering and if you go down that path it may be more difficult to switch to engineering. Making a sideways move within the organisation is perhaps a more likely path than moving into an engineering role in another.
And just a note, if the contract is 2 years fixed term, you can still leave at any time (provided you work your notice).

I wouldn’t lock yourself into a 2 year contract if you don’t want to do that job long term, you risk building a resume that makes it hard to go back to graduate employment level and if you become a professional rather then entry level you will need to demonstrate technical skills for professional engineering roles, and id be concerned you effectively shut yourself out from future technical roles if you did that for 2 years.