For me, I would construct a band that fits within the genre or genres of music I like. Also, if the lead guitarist plays with a rhythm guitarist, I give him one. I also keep in mind of any conflicts between the members. I also try to keep my band diverse. Meaning they can play a wide range of songs both soft and heavy. Anyway, here is what my ultimate band would look like:
Vocals: Lajon Witherspoon (Sevendust)
Guitar: Adam Zadel (Soil)
Guitar: James Root (Slipknot / Stone Sour)
Bass: Marco Coti Zelati (Lacuna Coil)
Drums: Shannon Larkin (Godsmack)
Lajon just has such a wide range of vocals. He can sing soft, hard, low, high, he can sing it all. I believe he is the best singer in metal today. He's who I try to model my voice after.
Adam Zadel is like the perfect guitarist for me. I am really into Alternative Metal. He plays both rhythm and lead (mostly lead). He can play soft, hard, or acoustic. His solos just fit just right with the song.
James Root is the man. He too plays both rhythm and lead, but mostly rhythm. His riffs in Stone Sour are awesome. Just like Adam he can play both soft, hard, and acoustic. I've only listened to a few Slipknot songs, but the ones I have the guitars are great.
Lacuna's bass always sounds great. Marco Coti Zelati really came out of his shell on the Karmacode album for Lacuna Coil. You can really hear the bass in that album and ever since then he's kept up the pace. He plays 5 string bass that he uses both a pic and his fingers.
Shannon Larkin. What can I say about him? He's freaking amazing on the drums. He can play double bass drums and single bass. He can play hard. He can play soft. He can play it all. Fantastic drummer.