Welcome to the site. When I was a kid and some one was doing a slab every able body fo miles came to help. They wood stake 2x4 like forms every 4 ft and screed it and when both side of that 2x4 was done it would be removed and the gap is filled. Today we see the pros just go be eye or feel or something and then use a big bull float to level it out. A few are very good at getting it good but the basements today are just not as flat as they were years ago.
When we did my nephews garage we built a 26 foot screed that looked kind of like a truss. The truck driver looked at us like we were nuts. But only two of us and it worked. He said that went better than most. After we got it close with that we used a bull float.
If yours is 15 foot one way just get a 16 foot 2x8 nail a couple 2x4's on each end for handles. One guy each end working it and a guy in the middle pushing it around with a shovel when you get a low spot or too much to screed.
The pros might be good by eye. I wouldn't trust my eyes doing it so seldom. Neal is right the more people the better but before the truck comes make sure everyone knows their job. Even practice a little as a dry run.
are a couple of 10' & 8' 2x4's too much $$$ ? plact the conc in sections - 10' x 7'6" w/2contraction jnts @ 90*,,, you could even use 1 x 3's to save on lumber costs,,, i don't know what the 2x4's in the middle mean but neither do you so we're even :beer: you only need to form the slab's perimeter,,, next time you're in an apron/vest store, pick up the basic conc book,,, BIG help seeing pics,,, suggest you get a couple friends to help when its time to place & finish,,, even better if 1 of them knows what to do.
since you mentioned 'screed', that's the 10' 2 x 4 that will ride on top of your level AND square forms which you will saw back & forth to level & place the conc ( you could also call the form a type of 'screed rail' - that's not correct but your 2 x 4 screed will be riding on top of the forms,,, for 4 pours 10' x 7'6, we wouldn't be using a bull float,,, 1 nice thing about smaller pours - IF/when you f-up, you only have to replace a small piece - good luck !
Villa:We've got a similar one we use that will do 12 foot in a pass.Vibrates and screeds all at once.Should not be to expensive to rent as they are not real expensive to buy as far as that type of tool goes.I think we gave around $2500 but have seen them for under $1000 so should not be to high of a rental.Well worth the money.Ours has a Stihl motor similar to a large weed wacker.
Personally I couldn’t see renting a power screed to do a 15 x 20 pad. Will he need the 16’ attachment to ride on the forms or will he be eye balling it as most of it was done in the videos. I doubt most rental places have that long of a base. If I was going to rent something I might rent a bull float and uses a long 2x6 to screed it. A first time DIYer would catch on quicker with a bull float and it would do the same thing the power unit would do as far as finish.