How should I build 25 x 31? Slab done

[geraldsgarage]

I bought my dads little old house a few years ago. While he was living he had a 25 x31 slab done.

I have been tinkering with the idea of finishing the project myself.

What route do you guys think would be the most cost effective?
Metal, concrete block or stick built?

And how should I do the roof?

Thanks for your input.

I'll post pics of the slab

Also you can see in the pics the two roll up doors.